I never see it happening.
Ultima is, as the name implies, the ultimate magic.
It's above meteor, and meteor is our lv3 limit break.

So unless they create 16 person parties in ShB and create a new limit break tier with it, which they're not going to do, I really can't see any reason they would let BLM cast it.

I also can't see a reason why the WoL/WoD would want to cast it considering the immeasurable destruction it would cause.
Sure the one Ultima Weapon uses is a supped up version, but the WoL/D is basically a living, walking aether nuke at this point.

Plus summoners would be jelly AF.