Mr Freeman has been MIA for quite some time now. He has now been found, as a playable character in the PC release of Renegade Ops. You will be able to play as the one free man and drive around in the Half Life 2 buggy. The game is due to be released on Steam on 14th October and will cost £9.99.
There has been a couple Half Life related news articles of late such as the supposed weapon info in DOTA 2 code, and Gabes Haiku (both of which I believe people are looking far to much into), and now Gordon is making an appearance albeit not in the game we have been waiting for, but perhaps this is Valve's subtle little ways of letting us know that he is in fact coming back. It must be in development by now, it's been what 3-4 years since episode 2, there is bound to be something in the works they aren't telling us about. My guestimation is for Episode 3 some point mid next year followed by Half Life 3 maybe Christmas or early to mid 2013.