*shifty eyes* I... actually do this in RP, along with the others in our little circle. Well, not so much new classes as just taking what we know about aether (and... other things) and using that knowledge to come up with different manipulations, different means, different abilities. It's how I thought up Antimony's unique brand of healing, as I had to devise a tradition that would have evolved apart from the Succor of the Shroud or the study of arcanima in Limsa.
It would probably piss off a lot of sticklers, I imagine, but oh well.