I feel that jump potions will be nice. At least for people who have been playing and have classes to 60. I currently have six classes to 60 and am working on a seventh. I hate grinding out levels but I make goals for it every day because there are only so many ways to level classes after you've gone through main story. So I would use a jump potion for my alts, or just for classes on an existing character that has made it through the story and quests already.
I feel that it would have to be a requirement that you've gotten a character to 60 though (or 70 when Stormsblood comes out because a lot of the time things are registered by max level) just to get a character to 50 or 60 but never really... max level.
I feel that it would have to be a requirement that you've gotten a character to 60 though (or 70 when Stormsblood comes out because a lot of the time things are registered by max level) just to get a character to 50 or 60 but never really... max level.