The Surface Pro runs on Windows 8.1, so any software made for that OS would work. Positive Grid have a Bias VST coming (hopefully standalone on Win8, too). You could run Overloud TH-2 (which is great), the full desktop version of Amplitube (which sounds about a million times better than the crap iOS version), Guitar Rig, Kuassa... or anything else that would run on a desktop PC.

It's sort of a best-of-both-worlds situation. The convenience and portability of a tablet, the power of a high-end laptop, even desktop computer.