OK...since I use both XM and GPS in my car (and rentals), I can offer some further thoughts:
1. I have a "Roady 2" (XM receiver) that I take along with me on trips for rental cars (I also have a Pioneer XM receiver permanently mounted in my personal car). In this application I leave the XM antenna up on the top of the dash, under the windshield. I've tried to have in sitting on the passenger seat...it didn't work. Similar problem with my GPS receiver...it won't work when it's sitting on the seat, but works fine as long as it's up on top of the dash near the windshield. It seems that in both cases, the receiver needs a clear, unobstructed view of the sky. The same is true when speaking of avionics...the GPS receiver is either placed on/near the windshield or it has an antenna that is (i.e. perhaps you've noticed the fins/bumps on top of planes...those are antennas).
2. Power is still a consideration. To my knowledge, there are only two types of Sirius/XM radios that are capable of being powered by batteries. The "boom-box" (and it may not work off of batteries), which for obvious reasons wouldn't work on a plane. Or the new portable models...hand-held units with internal hard drives. Models like the Roady 2, etc. require either a hard-wired power connection or the use of a cigarette lighter adapter...again, not practical on a commercial plane.

If the question is purely one of "can it work", the answer is yes. But you have to consider what you'll need to make it work. Power is consideration #1...you'll need a model that runs on batteries. Signal reception is consideration #2...I wouldn't count on good reception unless you have a window seat and are able to get the antenna up/aimed out the window.

IMO, from any practical/useable standpoint, on a commercial airliner you're going to have to use one of the portable units with programming saved to the hard drive. Based on my experience in cars, counting on getting a decent signal in an airliner would be unwise.