Windows RT is an "also-ran": Poor performance, high price, few apps. This platform is dead right out of the gate.
I think you are confusing Windows RT with Surface. Surface uses Windows RT but is compiled for ARM processors but Windows RT could compile for Intel as it always has.
Windows RT is a glorified Interop layer to Windows System calls that make it easier to program to system level API's and cuts down on the fat of having a .Net library for everything. Right now they limited it for these so called Windows store apps. I expect it to expand for desktop apps too. The performance should be better. It might stink a little on arm in some instances but that has more to do with porting windows system to ARM than using Windows RT.