They have said those restrictions are part of the beta, and going away soon.
Got a source for that? When I last looked into it, their site said it was a technical limitation and that there were no plans for creating a truly mobile receiver.
Eagle-eyed observers have noticed Starlink antennas on SpaceX's drone ships. So mobile capability is definitely already implemented, it's just not publicly available yet.
(Edit: And evidently some regular users are already beta-testing it too.)