Could you include src/materialsystem/shaderlib into the Source2013 SDK? It is included in the public ASW branch so I don't see why not...
All new branches like l4d/asw/p2/csgo/dota2 use embedded gameui (you moved it from engine into the client. So... could you include gameui into the Source2013 SDK and make it load from the game and not from the engine folder?
Could you fix the shader dll loading through the wildcard game_shader_generic*.dll. it works on 2006, 2007 and ASW.
Could you fix shader overriding? In 2006, 2007 and ASW you can override default shaders while on 2013 it doesn't allow that.