I often wonder why we've not heard a peep about Half Life (2: Episode) 3. I understand the concept of Valve Time, but even taking that into consideration we're closing in a decade since Episode 2 (and the whole episodic started with the claim that they could put out an Episode every six months). To have nothing, not even a single screenshot or even an official "yeah, we're making Pikm- er, Episode 3", in 8 years, seems really bizarre. At best we had a blurb about "Ricochet 2" as a thinly-veiled explanation of the HL3 lack of information in 2012. I understand that they want to get it right, but at this point they risk "Duke Nukem Forever" syndrome, where the vacuum created by the lack of information is filled by user hype and it will become impossible to meet gamer's expectations. (I don't expect the eventual HLF3 to be as poor as DNF was, though.)
My assumption as this point is that a small group is quietly tooling away at HL3 using the Source 2 engine (perhaps co-developing). Once both HL3 is more-or-less done, they'll sit on it and just keep the graphics updated. Right now Valve has so many things its trying (like SteamOS) and is still getting a ton of attention/money from Steam trading cards and marketplace, TF2 hats, and DOTA 2 that the company itself doesn't need HL3. Thus it will maintain and use HL3 as its "Final Fantasy" if it feels the company could be in financial trouble within two years. They could release it on the N-Gage and it will still sell millions of copies, so it's like one funds where you put something in and can't touch it for 20 years.