After Perfect Dark Zero, Rare had Chris Seavor and the Conker team at work on another Perfect Dark, also for Xbox, called Perfect Dark Core. Unseen64 has found concept art, 3D renders, and even video of this cancelled game -- and the other cancelled game it metamorphosed into. In this "more realistic" Perfect Dark game, players controlled a male character who accompanied a "smoking, flirting" Joanna Dark on her mission.
By late 2008, Core had been taken out of the Perfect Dark universe, and its team (cut down to three people) turned it into a mech FPS before the project was killed. It might not have been Perfect Dark, but it was probably really dark inside those mechs.