XNA on Windows 8? Really? From Microsoft? No. Check out MonoGame. However, I have to say that my opportunity is to focus on C++, but for you, MonoGame might be interesting.
What happened to XNA? I have no idea. One day I woke up and realized that no matter how much I whined about it, XNA was gone from Windows 8 Modern UI that will also work on the ARM devices. ARM is going to be big, so I will need to be ready for it.
Inside of C++, here lies the remains of XNA, and this is the principle things that many XNA designers moved to: XNA Math Library. Pretty major stuff. More later, and I have written a little about the vector math, etc. XNA ships as DirectXMath.
How about Xbox Live? I am getting started again with the //Build video