
Well, we don't have a whole lot of tribal lore, which is itself a complication. 
If I'm understanding what you're trying to do correctly, you want to have a character from some other tribe that wasn't one of the 26 tribes and is completely segregated from that system and the behavior of miqo'te as described in the lore posts. If that's the case, then while you can certainly RP whatever you like, my frank opinion is that it's a "bridge too far" from established lore. In addition to having to construct a lot of backstory to establish the tribe's nature, how it got separated, why it never got integrated into miqo'te tribal society or even mainstream Eorzean society, and the like, there's not a lot of grey areas in the lore to explain how that could easily happen. You'll also have a lot of explanation to do ICly when it comes up.
I guess my larger concern with the concept is that it's dodging a lot of the game's themes and concepts for miqo'te to a nebulous narrative end. That always gives me pause, because to me, it's essentially playing outside of the boundaries of the lore and getting deep into "special snowflake" territory. To go that far, I feel you that you need an extremely strong narrative justification for it.
Again, you can certainly play whatever you like, and I'll RP with anyone
, but my recommendation would be not to go down this road and instead stick with the lore -- because it's often so vague, there's a lot of room to play around in it.
Note: Please ignore all of the above if my summary in the second paragraph is wrong, because my thoughts are based on that. If I misunderstood, I apologize, and my commentary should be ignored.

If I'm understanding what you're trying to do correctly, you want to have a character from some other tribe that wasn't one of the 26 tribes and is completely segregated from that system and the behavior of miqo'te as described in the lore posts. If that's the case, then while you can certainly RP whatever you like, my frank opinion is that it's a "bridge too far" from established lore. In addition to having to construct a lot of backstory to establish the tribe's nature, how it got separated, why it never got integrated into miqo'te tribal society or even mainstream Eorzean society, and the like, there's not a lot of grey areas in the lore to explain how that could easily happen. You'll also have a lot of explanation to do ICly when it comes up.
I guess my larger concern with the concept is that it's dodging a lot of the game's themes and concepts for miqo'te to a nebulous narrative end. That always gives me pause, because to me, it's essentially playing outside of the boundaries of the lore and getting deep into "special snowflake" territory. To go that far, I feel you that you need an extremely strong narrative justification for it.
Again, you can certainly play whatever you like, and I'll RP with anyone

Note: Please ignore all of the above if my summary in the second paragraph is wrong, because my thoughts are based on that. If I misunderstood, I apologize, and my commentary should be ignored.

The Freelance Wizard
Quality RP at low, low prices!
((about me | about L'yhta Mahre | L'yhta's desk | about Mysterium, the Ivory Tower: a heavy RP society of mages))
Quality RP at low, low prices!
((about me | about L'yhta Mahre | L'yhta's desk | about Mysterium, the Ivory Tower: a heavy RP society of mages))