X-strike OP!
Unfortunately, this will lead to certain predetermined party comps based on the best combos which wouldn't be great.
We sort of have some aspect in the resistance debuffs, like Foe's Requiem into Flare though the rest are more passive.

I think a combo limit break would be awesome for 150% extra damage though.
Might be too much to ask since the combinations would increase incredibly as they introduced new classes.