Given that there is little existing homebrew code for xbox 360, I’ve sat down and ported Snes9x. After a day, mostly spent in debugging libxenon itself, I’ve had this running:
(Excuse the bad movie quality, my digicam sucks at movies.)
I used Snes9x GX, i.e. the Wii/Gamecube-Port, as a base. I didn’t use much of the GC-specific code, but it gave me a good idea of what functions I have to implement. I don’t yet have coded a UI, but it uses the GPU for scaling, USB for input (wired controller only so far), and runs on the bare metal (i.e. no linux, no hypervisor). CPU is still running at quarter speed, but there are no dropped frames.