I just believe it may one of that games. Not first. They say they went from SDK 2013 to "another Source engine". I really wanna know what "another Source engine" is.
Their statements are not clear.
They say they're forced to move "another" engine while free version is updated to SDK 2013. But they can't disclose this engine ATM due to licence agreement. Then they say it's not Source 2. Probably they're working with Unreal Engine.
Agreed. According to Steam Hardware & Software Survey, Windows OS still in the first place, while Linux OS not even 1%.
http://store.steampowered.com/hwsurvey
They will release the game for all platforms (PC, XOne, PS4, Linux/SteamOS) at the same time.
Edit: I'm so glad Kelly Bailey is back.