"But we couldn't release 3 ultimates per expansion if we did that!"
I bet a billion gil that would be their answer.

One of the things they feel proudest about is that "any job can clear ultimates." Very easy to do that when all jobs in each role play roughly the same with the same windows and whatever.

For the topic itself, yeah; just have a pve (casual) mode which uses pvp-like class skills/mechanics and pve (hardcore) for ultimates/savage.