Graphics API/SDKs are insignificant from a learning perspective, what's important is grasping the concepts and math that underpins 2d/3d computer graphics. Is your time wasted? Well, we don't know what you've been learning but I'm going to make an educated guess and say "of course not!". Sure, the syntax will be XNA-specific but the skills and knowledge is 100% translatable to other APIs/SKDs (well, obviously not the syntax). Don't dwell and get disheartened, rock on with XNA for the time being and worry about Win8 (non?)issues at a later stage.

Edit: sorry, the focus of your OP was C#, not XNA. Anyway, my point still stands, replace "graphics concepts" with "general programming concepts" and my point still stands.

Graphics API/SDKs are insignificant from a learning perspective, what's important is grasping the concepts and math that underpins 2d/3d computer graphics. Is your time wasted? Well, we don't know what you've been learning but I'm going to make an educated guess and say "of course not!". Sure, the syntax will be XNA-specific but the skills and knowledge is 100% translatable to other APIs/SKDs (well, obviously not the syntax). Don't dwell and get disheartened, rock on with XNA for the time being and worry about Win8 (non?)issues at a later stage.