I'm with OP on this, the FFT style advanced class system would rock, although I do foresee some issues with being forced to play somewhat unrelated classes to get to the one you want. Using the example given, I am first and foremost a Paladin on any game I play, but as suggested I would need to get to rank 20 on Conjurer, which as a mage class is something I can't stand playing. Considering a Paladin's playstyle is much closer to a Gladiator than a mage, this system would require some careful consideration to make sure people aren't forced to do things they find boring to get to "the fun part".