I've always thought of that, and talked to friends about it on FFXI. Kinda like a, let's say, 3hr ability, every job would transform into something. An example would be a dark knight becoming some kind of demon, etc. I would LOVE to see something like that, and the idea here exposed makes me want to see it even more.

Also, in FFVII Vincent would transform into beasts. It's not that CRAZY of an idea.