hmmm. i don't think multiclassing would work well in this game, with the way it's designed.
first off, you get a party of 6 plus 2 additional npc's that can be swapped around at will, so that pretty much covers all the classes.
second, the chars work best in this game if you specialize. they get very powerful.
third, it seems that the previous wiz games were designed to allow you to change class at will and create godlike chars.
fourth, if you multiclass, it becomes a much harder game, and i think it's already hard enough, thank you very much! they have a fabulous level system, it makes you focus and plan things out. believe me, if you misplace points in a couple of level ups, you will feel it!
i love dualing and multi classing in other rpgs i have played, but i find it refreshing to play one class and play it to the limit in this rpg. they have done it right. everything in this game rocks, and i think it's better for having pure classes.
and i very much doubt if they will redesign the game for multi-classing, as they have given up their souls just to get this one out the door.