This has got me thinking. Surely GW will describe them later than sooner, but what if they just unite them in large books much like with the Disciples of Tzeentch? Especially really small and clearly auxiliary factions, like Deathmages. It's hardly to imagine an army of wizards really, but as a part of some larger force it can be pretty good. It can be easier than depicting them all one by one. What do you think?