Alpine has announced that their newer Ai-NET series head units will now support either Sirius or XM satellite radio (although not both at the same time, I don’t think). Really, all it means is that the satellite receivers use the generic Ai-NET interface to connect, much like the Alpine KCA-420i iPod Interface, so you can add components piecemeal as you see fit. You can use one of the satellite receivers with the KCA-420i units in the same system, though, so maybe you could have both satellite radios as an option. (Thanks, Aaron!)
https://gizmodo.com/alpines-kca-420i-ipod-interface-available-in-september-17513
Alpine is the very first to offer Sirius or XM!
[Alpine-USA]
Update: I have confirmed that you can have both XM and Sirius at the same time. Sounds good.