There's a decent class idea thread
here that discusses various possibilities for a class centered around range heavy / melee light DPS of various flavors. I liked it for the Dark Ranger and Warden specs, harkening back to the WC3 heroes of the same names.
It would cover a ranged physical damage role that only the hunter holds right now, and its sufficiently different from the hunter.
I'd like to see some kind of hybrid ranged/melee DPS spec, which is something we don't really have at the moment - a class that can perform melee combat and ranged combat as needed, even having some kind of mechanic that necessitates switching between the two. Perhaps melee resources only regenerate while in range move, and vice versa. I think Runemasters could work like this as a kind of rogue-shaman-death knight, although they might be too similar to monks at this point - Runemasters have such a cool visual appearance though (tauren ones, anyway).
If we're going into a Legion-themed expac I still think there's possibility for a demon hunter class. I'd lift the Demonic Fury mechanic from warlocks and use it to to fulfill various roles depending on spec. In the end a demonology warlock would be to demon hunters like a feral druid is to rogues. Maybe demon hunters could have a melee spec, tank spec, and the melee/range hybrid DPS I mentioned above.