a few points. 1 is i believe officially sirius bought xm. 2 is sirius' CEO is going to be the head of the combined company. my company went through a merger a few years ago. the smaller company officially bought the larger company. the company is officially headquartered at the smaller's old headquarters. we did keep their CEO but he actually came from our company before going there. guess whose name and products are no longer around? it's not the smaller company. 3 is that, in order for the merger to be approved, they had to agree that they would allow content from one provider on the other's hardware (i think it starts at $5/month extra for the additional content), and all hardware is capable of doing that. maybe they'll phase out one hardware type but for a pretty long amount of time they'll have to have both hardware systems running, both because of the number of subscribers already on both service (can't just say to millions of people sorry see ya later as a new company), what they had to agree to for the merger, as well as things like sirius' lifetime subscriptions that they sold.
what i'd do is wait a little bit for any new hardware to see if manufacturers come out with units that receive both formats natively. hardware development for both has been relatively stagnant while the merger was in flux so i'd say hang on a little longer to see what happens now