[Butz]

Mmm, yes, so you could have another kingdom-esque group where people are supposed to RP but they don't.
Then you'd get the people who would go to join, and they'd be like "But I'm a high ranked mage in So-and-so kingdom, and I'm level 27-bajillion! I can shoot fireballs out of my eyes and make you think you're a pink bear hula dancing. "
Errr...well, maybe not that far..
Anyway, in summary, I don't think it's that great of an idea. What you're basically asking for is an All-Mages kingdom. :-/