Seriously, this. I tried for days to register on Lemmy. One day I was mid-registration and the button was just spinning, doing nothing, so I came over to kbin, registered and started using the site. Lemmy never stopped spinning. No thanks.
Though I suspect that means that either the clients are gonna start visibly stuffing instance names at the end of the username -- maybe some abbreviated form of instance name -- or there's gonna have to be some other effort to stop users from pretending to be other users and creating problems.
You can distinguish between users by their user icon, but that's user-selected, not assigned by the server, so a malicious user could just clone another's.
It was doing the same thing for me but I checked my email and there was a verification, once I completed it my registration went through. It didn't actually tell me it was sending an email which is probably a flaw but it seems that's the missing piece.