I believe it has been speculated before that demons and such will be getting an overhaul, and hopefully become more cooler than they are now.
What WANT though is a more fleshing out of religions. I'm not big dev note nerd, and perhaps it's been mentioned somewhere, but i want religions to be a much more dominant force over the behavior of civilization.
What I mean by this is, as it stands, everyone just spins the "wheel of deities" and gets to worship one at random, and that particular religion has no effect on that individual whatsoever. They never pray or carve they're personality after their god. Every god is just part of a random pagan tossup and doesn't really represent anything.
Gods, or perhaps, religions, in real life represent sets of morals and beliefs. It would be awesome if religions had the power to influence a race's ETHICS. Elves who worshipped a god that symbolized certain things like open-mindedness and metal might convince those elves to not be angry at tree murder and wear metal armor. Goblins that worshipped a god of pacifism and peaceful solutions might not be angry or aggressive towards everyone.
Even better, their can be inquisitions and holy wars depending an what is the most dominant religion. That would be AWESOME.