I think buggering about with level squishes or new levelling systems once we reach Lv100 is a horrible idea that tries to solve a relatively simple problem with an obtuse solution. We have an established character progression path that flows relatively smoothly (if not a bit too quickly). 50 levels on the base game and then 10 levels per Expansion, and that works fine.

Other RPG's have level caps beyond 100 and its not without precedence in FF either. The only good argument for not going past 100 I've seen is that it could be daunting to newcomers to see that they have 110 or 150 levels ahead of them. But, by that point they'll have the base game and 6+ expansions to make their way through anyway which would be a far more daunting prospect than the levels.