In the hlcoders/hlmappers mailing lists you can get little bits and pieces of the Source 2 picture sometimes. Someone asked about having the Source SDK on non-Windows platforms with the 2013 update and the response was "no, but the toolchain for Source 2 was designed to be multi-platform from the start so that will be the case there".
My guess is Source 2 is really a large rewrite with next-gen platforms in mind. Everything about the current Source engine (Source 1) reeks of outdatedness, such as pathetic dynamic lighting, lightmapping, very heavy use of BSP (even though it's a largely outdated technique I really like brush modeling), and the truly AWFUL asset importing workflow.