Nothing I've seen, but I do know that downloading songs over wifi put a big beating on my Ultra battery, and wifi is more efficient for transferring data than cellular. I'm sure the Ultra has the horsepower to do it but it seems like the battery would be exhausted pretty quickly if Apple allows that function. Even on my phone I use that hotspot feature pretty regularly (well, every week or so) and checking the battery stats afterwards it also hammers the phone battery too.
I'm guessing it'a a no go based on the current watch tech. Hopefully someone will prove me wrong.