Speaking to NeoGamr, Valve revealed that over four million units of Portal 2 have been sold worldwide across PC, Mac and consoles. The original had also managed to shift similar figures, notwithstanding Steam sales which should push it to higher figures.
Available now is the Perpetual Testing Initiative DLC for PC and Mac versions of the game. It adds a level editor with full Steam Workshop integration. I wouldn’t hold my breath for a console release.