We have not started any work on displaying weather in any way. It will not be part of the upcoming multi-leg flight planning that will be out in just a few weeks.
Because of this, we can't commit to supporting any specific hardware or connection method, and I don't know if it will be feasible for us to support the music side of an XM tuner.
Wish we had a more solid answer for you at this point, but we don't want to make any promises we can't keep.