Priests and Wizards as separate classes

[JusticeZero]

There's also the way that it appears that 5E is going with from the rules posted - prepare a small subset of augmentable spells each day, then cast them spontaneously. Seemed like an interesting idea, if I still cared about wizards and clerics.. which I don't.
I might also recommend looking into the Generic Spellcaster class for 3.x. That basically just says "Start with a Sorcerer chassis. Pick your spells known from all of the T1 lists however you think fits." Swap that for all your spellcasters and you now have one "magic user" class with a lot of variety, since everyone is packing a limited but idiosyncratic personal list.
Also, reserve feats are nice things.