Might an aligned superintelligence force people to "upload" themselves, so as to more efficiently use the matter of their bodies?

Matter in the body is probably not the main thing, but rather the resources needed to support and benefit the person. It takes much less resources to give an emulation a good life than an embodied person

Aligned systems as a rule do not to force people to do things that they don't want to do. If it’s forcing that it’s probably not aligned.

In the long run, future moral entities might all/mostly be emulations, but there is no rush to get your particles. There are plenty of stars.