In a post on the official World of Warcraft forums, Blizzard community manager Zarhym came out and said the new MMO was in fact an original IP, saying, "We have nothing to advertise for the new MMO because it's a shell of a game thus far. We've already stated it'll be a brand new franchise, which means the lore, art, and game play are being developed entirely from scratch. It's an overwhelming process, but a process through which we excel. Our track record supports this." While it's no press release or big event reveal, this is certainly the closest we've come to someone officially with Blizzard saying that, yes, it's not a previously created franchise.
So now that speculation on whether or not it's a new IP is over, we can begin to speculate on what genre this new IP will be! Science fiction, steampunk, cyberpunk or another fantasy setting? It's hard to say, although our hopes go for something decidedly not fantasy since Blizzard has already spent plenty of energy in those genres up to this point.