Since mobile high speed broadband is becoming more widespread it would make sense to add it as an option in RR. I'm no programmer but I don't think it would be too difficult to implement using something like uSirius(
http://www.millardsoftware.com/usirius)
Given that if you come into a low coverage area for your cell provider you'll lose sat radio, but that probably won't happen too often.
Another plus would be the sound quality would be better than from the actual sat transmission. I've read a few places that the audio streams from sirius are variable and broadcast anywhere from 25-50kbps while the internet streams @ 128kbps.
Just a thought...