Well, we have "Limit Breaks" already - the TP attacks are nothing else.

Problem is that they are
a) too frequently used and
b) too weak

to leave any impression. It's just pew-pew TP moves back to back, and
not the big "BOOOOOMMMM" you expect from a real Limit Break. How
long does it take you to teach 1000TP? For me, it's around 3 seconds.
That's a rather puny limit, if you can break it in 3 seconds ^.^/

2-hour abilities, while cool, have a problem: They are too powerful,
almost game-breaking. So either you tune Boss fights to be so hard
as to compensate for everyone using his 2-hour-ability (frustration
guaranteed) or tune them too easy so that you can zerg the bosses
by using everyone's 2-hour-ability. Both are not satisfactory solutions.