WotLK Client with new Models also to receive newer graphical effects.
So if the title isn't clear enough, Cataclysm, Mists, WoD and legion all added new animations, spell visuals, etc. Things of note that come to mind are:
-Basically all shaman spells (mostly cataclysm spell effects for lightning and water spells)
-Many mage spells
-Many priest spells
-class specific casitng animations
I don't know how hard it would be to implement these graphical improvements to the WotLK client, or even BC client for that matter, since I have absolutely no experience with how the game works code-wise. But I think it would be great if we could get this!
-A new player to Warmane that noticed the WoD models in wotlk!