I've been advised by my local avionics shop that only the GTN 750 supports the full functionality. I.e. The GTN 650 doesn't support Weather Radar. If that's not correct please let me know.
With the limited panel space available it would be nice not to be forced into the large size of the GTN 750. With the G3X supporting SiriusXM I wouldn't think it would be all that difficult to support the GSR 56, I could be wrong though.