According to 1UP, Sigil - the team working on Vanguard - has acquired the rights to develop a Marvel Comics MMORPG for the XBOX 360 and the PC. This further confuses the state of superhero MMORPGs, as it had previously been announced that SOE acquired the rights to - and is developing - a DC-Comics based MMORPG.
It would seem that if the reports of Sigil making the Marvel MMORPG are true, then they must be publishing it through Microsoft who aquired the exclusive rights to that license earlier this year. In that announcement, it was said that the Marvel MMORPG would be made exclusive for the Xbox 360, so there is some discrepancy between the original announcement and the 1UP story, which indicates it will come for PC as well.
To lend some support to the announcement, the Sigil site has a note dated September 16, 2005 that welcomes Bruce Harlick to their team as a Senior Game Designer. Given Vanguard's advanced stage of development, such a hiring would seem unnecessary unless another game was on the radar. Although, this is pure speculation.