Yeah, absolutely!:
Human
Blood Elf
Worgen (assuming the toggle is like 90%+ under their control and they generally stay Human – it’s just a curse)
Ok, why not?:
Night Elf
Dwarf
Unlikely, but if there’s a solid connection, maybe?:
Draenei
Orc (assuming the character model portrayal of Orcs)
Never!:
Gnome
Troll
Undead
Orc (assuming the cinematic portrayal of Orcs)
Pandaren
Tauren
Worgen (assuming the toggle is < 90% under their control or they prefer to stay in Worgen form)
Gnome could -potentially- move up a bracket depending on what sort of depiction we’re going for. Some art makes them a bit more acceptable, but as they appear in game, No.