As with all of this "black ops" stuff, there's not too much to get excited about yet -- the reason these companies haven't officially announced any of these games is not only because their release is likely years off, but companies will very often develop games that they don't end up releasing at all (case in point, as Blizzard fans well know). So the reason we don't know anything about Blizzard's next MMO is because Blizzard likely doesn't know anything about it yet either -- will it be a successor to World of Warcraft, a much-awaited Starcraft MMO, or a completely new IP from the company that has conquered the MMO genre? Odds are that right now they're working on engine and code mechanics, and the final form that the project will take is just a gleam in a Blizzard employee's eye.
Still, it's fun to dream, isn't it? With the coming release of Wrath (and Diablo III and Starcraft II coming into focus), we've got plenty of Blizzard games to look forward to as it is.