It's not news that ZeniMax Media, the parent company of Bethesda Softworks and now id Software, is working on an MMO. The company has been hiring at ZeniMax Online to develop a "next-generation MMO" for some time. But the continued legal battles between Interplay and Bethesda over the rights to the Fallout brand have brought some (albeit small) details to light about that upcoming MMO.
For one, it's not based in the Fallout world. It would've been pretty natural to assume it's not a Fallout-based online adventure because Interplay themselves retained the rights to a Fallout MMO after Bethesda bought Fallout, but in latest court transcripts from Fallout community site Duck And Cover, it's been confirmed Bethesda (and, by extension, ZeniMax) is not developing a Fallout MMO.
In the words of Bethesda's lawyer, they're working "on something else."
What that "something else" is remains a mystery. It's been over a year since Fallout 3 was released and Bethesda has not announced either a follow-up to Fallout 3 (then again, we haven't seen an official reveal of Fallout: New Vegas yet) or a new installment in the Elder Scrolls series. According to VG247, the same website alleging the PlayStation 3 motion controller is named Arc, the as-of-yet unrevealed MMO is, in fact, the next game in the Elder Scrolls series -- an Elder Scrolls MMO.
Bethesda is due for an announcement. Maybe it will be this MMO. Stay tuned!