
Well I certainly took my time on this post, but really thanks everyone. I'm loving all of these various view points you've all got here. It really gives me a good idea on the state of affairs here. 
Though I should say bout the Scythe bit . . . that was more of a pure example of the potential kinds of unorthodox weaponry rather than a hint of what I'd like to use. Its tool I'd think that's very feasible to exists in this timeline despite we've yet to see one in game(or least I've yet to see anyone tending the fields, period). Its simply not often weaponized by traveling adventurers, though not too much is stopping a capable adventure from trying to do so.
But to get a little more personal: I designed my character from the beginning to be a specialist in greatswords, even though said class isn't available as of yet. Greatswords have always been my weapon of choice in RPGs when it has been available as they tend bear the Mighty Glacier playstyle I prefer. And while I may be largely unfamiliar with Final Fantasy as a whole, I do believe it's only a matter of time before a my sought after class arrives that efficiently wields such a massive blade. Probably months and months away, but it will surely come if what I've researched on XI is any foretelling of what Square is willing to do on the MMO side of things. Till then, my character isn't above utilizing other tools outside his accustomed proficiency to get the job done(dabbling into the other classes like the pugilist). So that way I can still play the current classes and it won't suddenly be awkward or OOC. But now I look back and realize a slight issue.Â
Assume the day does that a greatsword guild is founded and begins to accept members. Why after months of mastering/experiencing numerous forms of combat would said character suddenly decide to not only join up but hold its craftsmanship above all of his previously honed and mastered skills? Especially when he usually refers to his other weaponry as mere tools for his work. Sure he'd pick it up to advance his combat knowledge, but I can't find motivation here as to why the greatsword would become his main focus of all of his combat skills instead of simply another tool for the job. I mean to me, when you call a certain weapon type your specialty above all others, there's usually some form of personal attachment or bonding to said weapon. Dubs little snippet is evident of that, surely he and his Grymgohta have been through a lot together to share that kind of relationship. At least I'd think so. I want my character to have a much deeper appreciation for the blade over the rest of his gear, and the best way I believe said goal can be accomplished is for said sword to appear in his early life. Which would have to be before greatswords would ever see widespread usage among the adventurers of Eorzea and before my character would have easy access to the various weapon guilds. While I'm still narrowing down exact descriptive feelings beyond "the one true companion that has stuck with him through and through", the placement should at least lead to some reasoning as to why he would hold such a weapon in greater standing than his others.
As I am nailing down the possibilities of how said blade is acquired, a Garlean origin for my greatsword seems likely as it would allow my character the earliest opportunity to acquire it. Which may or may not imply a gunblade modification to the weapon that I mentioned earlier. And I'm not at all too crazy about that, as honest as I can be. So you slapped a longsword onto a gun and called it technological superiority, goodie for you Garleans, I hardly see the marvel in it at this moment. Â Regardless, taking to account with how much the Garlean Empire likes to marry firearms and blades, I'd find it somewhat difficult to justify why said greatsword would lack such a thing. I would probably limit the gun bit to being something with shorter range and slow/not-spammable like a shotgun or a musket just to emphasize its melee proficiency over ranged fire power. But if its possible to lack said attachment and make sense to be of Garlean craft, I certainly wont mind taking that route for further balancing. And as I stated in the OP, such a weapon would probably have no action trait support and many other shortcomings due to its experimental nature.
More or less, I'm pretty much just poking around trying to determine whats acceptable in the community and what constitutes as overboard. I do think understand the difficulties as addressed as such, some I was aware of but there was some information that got me to think a little more. I have little issue of mentioning the blade from time to time as I am usually descriptive with actions, that large slab of steel is bound so clank around as he moves. I will probably attempt to design said weapon a simply shaped as possible so it so it wouldn't be so difficult to describe. I also have little intent to attempt wield a different weapon type and pass it off as said greatsword as I would usually simply imagine in on his back along with his usual existing in-game weaponry. If it would however be better for the community leaving the blade in the care of a retainer or restricting usage of it till the widespread release of greatswords; so be it. But I feel that the weapon needs at the very least to have an existence in the backstory. Alternatively, my character does very well wield the existing weapons(swords, axes, baghnakhs, lances) along side with the custom greatsword, so it would certainly wouldn't bring about RP awkwardness if random bystander decided to comment on one of my other weaponry instead. In the end, I do understand if it really pushes someones buttons a little too far and ends up alienating me from a number individuals. I can at least take pride that there are some individuals here that are willing to RP with me in light of my abnormal character decisions; and that's something I can live with.
Well that was a lot . . . soo obligatory TL;DR : I like greatswords, its what my character was designed around. I'd like for said greatsword to appear in his early history for bonding purposes. Its origin may be garlean and may have the gun- attachment that I'm not too crazy about. I will take great care into ensuring it has the proper drawbacks to its already perceived advantages such as no action traits or class support. And I believe I can combat the negatives presented in this thread of custom weaponry and calmly adapt to the situation if it proves hazardous in RP.
Really, thanks again for all of these replies.

Though I should say bout the Scythe bit . . . that was more of a pure example of the potential kinds of unorthodox weaponry rather than a hint of what I'd like to use. Its tool I'd think that's very feasible to exists in this timeline despite we've yet to see one in game(or least I've yet to see anyone tending the fields, period). Its simply not often weaponized by traveling adventurers, though not too much is stopping a capable adventure from trying to do so.
But to get a little more personal: I designed my character from the beginning to be a specialist in greatswords, even though said class isn't available as of yet. Greatswords have always been my weapon of choice in RPGs when it has been available as they tend bear the Mighty Glacier playstyle I prefer. And while I may be largely unfamiliar with Final Fantasy as a whole, I do believe it's only a matter of time before a my sought after class arrives that efficiently wields such a massive blade. Probably months and months away, but it will surely come if what I've researched on XI is any foretelling of what Square is willing to do on the MMO side of things. Till then, my character isn't above utilizing other tools outside his accustomed proficiency to get the job done(dabbling into the other classes like the pugilist). So that way I can still play the current classes and it won't suddenly be awkward or OOC. But now I look back and realize a slight issue.Â
Assume the day does that a greatsword guild is founded and begins to accept members. Why after months of mastering/experiencing numerous forms of combat would said character suddenly decide to not only join up but hold its craftsmanship above all of his previously honed and mastered skills? Especially when he usually refers to his other weaponry as mere tools for his work. Sure he'd pick it up to advance his combat knowledge, but I can't find motivation here as to why the greatsword would become his main focus of all of his combat skills instead of simply another tool for the job. I mean to me, when you call a certain weapon type your specialty above all others, there's usually some form of personal attachment or bonding to said weapon. Dubs little snippet is evident of that, surely he and his Grymgohta have been through a lot together to share that kind of relationship. At least I'd think so. I want my character to have a much deeper appreciation for the blade over the rest of his gear, and the best way I believe said goal can be accomplished is for said sword to appear in his early life. Which would have to be before greatswords would ever see widespread usage among the adventurers of Eorzea and before my character would have easy access to the various weapon guilds. While I'm still narrowing down exact descriptive feelings beyond "the one true companion that has stuck with him through and through", the placement should at least lead to some reasoning as to why he would hold such a weapon in greater standing than his others.
As I am nailing down the possibilities of how said blade is acquired, a Garlean origin for my greatsword seems likely as it would allow my character the earliest opportunity to acquire it. Which may or may not imply a gunblade modification to the weapon that I mentioned earlier. And I'm not at all too crazy about that, as honest as I can be. So you slapped a longsword onto a gun and called it technological superiority, goodie for you Garleans, I hardly see the marvel in it at this moment. Â Regardless, taking to account with how much the Garlean Empire likes to marry firearms and blades, I'd find it somewhat difficult to justify why said greatsword would lack such a thing. I would probably limit the gun bit to being something with shorter range and slow/not-spammable like a shotgun or a musket just to emphasize its melee proficiency over ranged fire power. But if its possible to lack said attachment and make sense to be of Garlean craft, I certainly wont mind taking that route for further balancing. And as I stated in the OP, such a weapon would probably have no action trait support and many other shortcomings due to its experimental nature.
More or less, I'm pretty much just poking around trying to determine whats acceptable in the community and what constitutes as overboard. I do think understand the difficulties as addressed as such, some I was aware of but there was some information that got me to think a little more. I have little issue of mentioning the blade from time to time as I am usually descriptive with actions, that large slab of steel is bound so clank around as he moves. I will probably attempt to design said weapon a simply shaped as possible so it so it wouldn't be so difficult to describe. I also have little intent to attempt wield a different weapon type and pass it off as said greatsword as I would usually simply imagine in on his back along with his usual existing in-game weaponry. If it would however be better for the community leaving the blade in the care of a retainer or restricting usage of it till the widespread release of greatswords; so be it. But I feel that the weapon needs at the very least to have an existence in the backstory. Alternatively, my character does very well wield the existing weapons(swords, axes, baghnakhs, lances) along side with the custom greatsword, so it would certainly wouldn't bring about RP awkwardness if random bystander decided to comment on one of my other weaponry instead. In the end, I do understand if it really pushes someones buttons a little too far and ends up alienating me from a number individuals. I can at least take pride that there are some individuals here that are willing to RP with me in light of my abnormal character decisions; and that's something I can live with.
Well that was a lot . . . soo obligatory TL;DR : I like greatswords, its what my character was designed around. I'd like for said greatsword to appear in his early history for bonding purposes. Its origin may be garlean and may have the gun- attachment that I'm not too crazy about. I will take great care into ensuring it has the proper drawbacks to its already perceived advantages such as no action traits or class support. And I believe I can combat the negatives presented in this thread of custom weaponry and calmly adapt to the situation if it proves hazardous in RP.
Really, thanks again for all of these replies.