Services like finding a stolen car and onstar are not very likely at this point. Satellite radios are receivers only, and not approved for transmitting. In order to locate a car, police would need to receive a signal transmitted from the satellite radio. In addition, the satellites are not designed to locate sdars radios.
Onstar requires two way communication. Sdars does not have that yet. To get such a plan in place will take two years at least, and likely need FCC approval.
This is not to say that it is not possible. It is. However, there would be a lot that needs to happen in order for it to be real. There are more pressing issues that need to be dealt with first. Dreams like this will be on the back burner.