I would love to see XBMC content listed in the HD Guide so that you can browse movies/music right on your iOS device and then pick one to play on your TV. I’m fairly certain that there are quite a few XBMC users out there and all of them using Roomie would definitely love this feature.
XBMC exposes a pretty detailed JSON interface (wiki.xbmc.org/index.php?title=JSON-RPC_API) so there is something to build off of.