Whatever it is, I sure hope it ends up taking a different path than WoW and not just using one of their other IPs and making a WoW-esque game out of it.
I'd prefer single-player ("offline") RPGs stay along the lines of Elder Scrolls/Final Fantasy/Fallout/Baldur's Gate. The MMO gameplay is really only best suited for MMOs themselves.
Open world, definitely. Some instancing is fine, but a major feature of an MMO I like best is a vast, open landscape. Loading screens really detract for me so the least the better, but instancing for some quests and dungeons/raids is fine.
Even though I wasn't a fan of the game, the Bear Shaman class in Age of Conan was exactly the kind of class I enjoy most. Not surpsingly I also like the Captain from LOTRO.
LOTRO did the hunter class pretty well, IMO. I'd like if it had a bit more focus on druidic capabilities and the tracking system sucks, but otherwise it's a pretty solid representation.