I think individual Limit Breaks could be interesting.

Since, they'd feel better to use, so it's not just 1 person gets to have fun using the cool flashy limit break. It'd fit better with capturing the feel of previous FF titles which had characters having individual LB's. It'd also stop lots of issues with various things incidentally becoming DPS boosts by their LB generation capacity (Things like fluff shielding from WAR/PLD AoE shields don't really help keep people alive, but they do provide a bunch of LB generation which means they're a DPS gain)

The main issue would be the amount of balancing they would require to make work. So that each class has an appropriate damage LB for how fast they generate LB gauge, which is then factored into their overall DPS. Potentially also making different jobs have different LB's as opposed to the current role based generics (Even if the level 3 variant has unique animations per job, their effects are all the same within a role)

Overall, I think it could be a beneficial move to make. Just a matter of, will it be worth the time of the developers to implement and balance?