"I doubt we're going to do another IP," Carmack told OPM. "We want to support Wolfenstein, Doom and Quake -- and hopefully we can add Rage onto that. ... Obviously, if Rage is a success then we'll want to do a Rage 2." Considering the lengthy development cycles at id (evidenced by the currently-MIA Doom 4) who knows when the next new IP will bubble out of the company?
Especially with that Commander Keen reboot getting in the way, right?