Cool on paper but considering current balance issues I don't think adding special effects on the LB's of certain jobs would be advantageous to that balance..

As for the personal LB suggestion - many jobs do have "personal LBs" in a sense already..

Benediction.
Holmgang.
Hallowed Ground.
Living Dead.
Perfect Balance.

Just to name a few...

All you are suggesting with personal LB's is to add another skill tied to a "cooldown" of sorts (in the way that you have to fill the LB bar up before using it) that gives you a one-off strong "whatever your role does" action.

I mean it's cool in theory though you might as well just give every job a new high-CD skill without having to add another battle mechanic to the game.

Limit breaks are party wide for the very reason that it's a "shared" action that can be decided upon how to use it.. Giving everyone a personal LB is just the same as giving everyone a new high-CD skill.