System Link just found the trademark, which extends to a few domain registrations -- all signs point to this being an unannounced game right now.
Everything else at this point is speculation, though we're fairly certain that Bethesda and id aren't involved -- both have Skyrim and Rage to worry about at present. Zenimax does own several other studios, however, including Machinegames Sweden AB, Tango Gameworks, Arkane Studios and Vir2L Studios, any of whom could be tapped for this project.
Finally, let's not forget Zenimax Online Studios, the parent company's MMO developer formed in 2007 ... right around when the trademark was first filed. Coincidence?