I think a spec quest would be great. I would also be fine with Glyphs to change all my holy spells to shadow colors. I can pretend my levitate sparkles are the negative interaction with the light is lifting me up. The other spells are just too light based.
I also think shadow priest, affliction lock and maybe something like a void mage spec should be a new class. It could be a class that focuses on damaging and syphoning life to heal party members. No direct healing.