According to a 10-K financial report filed earlier today, it appears that Interplay - who were supposed to have been developing a Fallout MMO - might instead have the project canned by Bethesda.
The looming action (which has not yet been made official, but is still likely enough to warrant Interplay filing about it) stems not from the game's rights - which Interplay picked up fair and square - but from the game's progress. Or lack thereof.
Fallout IP owners Bethesda allege that, as part of the deal in which they bought the rights to Fallout (but left the MMO rights for Interplay), Interplay were supposed to have commenced "full-scale" work on the title by April 4, 2009.
Interplay were also supposed to have secured funding for the development of the game. Bethesda claim that neither of these conditions have been met.
As a result, Bethesda are seriously considering "[terminating]the trademark licence agreement" currently in place between the two companies.
If Bethesda choose to go ahead with all this, and win, Interplay would lose their rights to produce a Fallout MMO, which may explain why an Interplay MMO is sticking with a "Project V13" code name instead of officially coming out with Fallout MMO branding.
For what it's worth, Interplay "adamantly disputes these claims". We've contacted Bethesda for comment, and will update when/if we hear back from them.