I have a feeling:
1. The are going to focus on OpenGL with this engine. They've already ported much of their Source engine to Mac and now Linux. I just have a feeling that they are going to go ALL-IN on OpenGL this time so it is completely platform independent. I think it'll even have a Source 2 - Mobile Edition Engine for iPhones and Android devices. They want to be able to have their games/interface on all aspects of desktop and mobile computing environments. One engine to rule them all.
2. I think that they work with a partner manufacturer to release a Steam Box. They've not only created Steam Linux, but they've created a "Big Picture" button for easy viewing/navigation from the living room. They want to compete against the PS3 and the XBox. If they can create a distro and/or sell a little linux box themselves for the living room, they'll do it. There's huge potential for the living room.
3. With this push of these two huge ventures listed above, what better way to draw excitement than to release Half-Life 3, Portal 3, Counter-Strike 3, Left 4 Dead 3, and Team Fortress 3 all at the same time.
There's a reason Source has been lagging behind some of the other engines lately as well as games that should have been released a long time ago. They have huge plans in the pipeline that have me very excited, but it's taking a lot of retooling and coordinating. It's definitely not as trivial as updating the engine for DirectX 11 features.