AMD cards don't support CUDA.
That's correct, AMD has announced that they support OpenCL as the GPGPU language. And OpenCL is an open standard as opposed to CUDA (NVidia proprietary).
which one could be running wesnoth in the future?
Forget the "future". Maemo already runs Wesnoth, and quite well at that.
Our informal mission is to improve the love life of operators worldwide. -- Peter Behrendt, president of Exabyte