I may be alone on this, but I'm hoping that the MMO rumor is true. Lets face it a quality MMO, or multiplayer aspect is long over due, and I would trust this company to come up with something good, that wasn't just another WOW clone. That being said, I wouldn't want them to give up on the single player campaigns, (which I doubt they ever would), guess I'm greedy, I want both.
If there's an Elder Scrolls MMORPG it will be developed by Zenimax Online Studios, not Bethesda. Bethesda would no doubt consult but the developement itself would be handled by ZOS.
However this does mean its possible for an Elder Scrolls MMORPG to be in developement along with TES V.