uhh you can run linux on it! you can write whatever code you want for linux, and run it, unsigned on the xbox...
is there any reason you couldn't set up an xbox 360 as a full media centre with mythtv and DTB capture via a usb dongle?
we might need more graphics acceleration for that
you can also run emulators under linux, as soon as they work out 3d acceleration on the 360. and if it's compiled for ppc