According to most of my research the easiest way to port a Source 2007 or Source 2006 engine game is to simply port it forward to the Source 2013 engine.
Once that is done, it requires almost no changes to make it run cross-platform. This makes Mac and Linux ports very easy. Console platforms, with the exception of Steam Machines, are a little more difficult, because you have to secure distribution, but they still aren’t that hard to port to, especially once you have Mac and Linux support down. (Wii U and most other consoles except XBox do not have Direct X libraries, so shaders must be compliant with Valves HLSL transcompiling library, and not use any added routines that rely on DirectX or Win32 specific libraries. You are already doing this if you have ported to Linux. That just leaves shipping default controller configs and licensing and distribution issues.)