Unfortunately, XNA is not supposed to be used as a target framework in Visual Studio 2012 for both Windows Phone and Windows RT, you are supposed to use DirectX for that.
You can still create applications using XNA, nothing has changed there. But you don't have a project template nor it is supported to be used that way.
But if you prefer XNA as a framework, you can try
MonoGame which is an open source implementation of XNA and you can easily build XNA based games for Windows RT with it. Keep in mind that DirectX is available only in C++ project types. If you want to use it in C#, you'll have to either write your
own wrappers or use some third party like SharpDX.
My blog: Toni codes .NET
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