Something that might help is a (preferably semi-official) page to direct people to for signup, where it randomly directs you to sign up for any participating server. You could have participating servers give some kind of feedback on how much signup pressure they’re seeing to slow down incoming rates when they have too many new users too quickly (wouldn’t resolve something like Reddit dying, but might be generally useful to turn down extra redirects to you if you’re getting an influx from elsewhere).

The issue is that until accounts are more portable, getting sent to a bad server isn’t great. Ideally there would be a mechanism for users to mirror their account to a second server so they don’t lose everything if a server goes down as well.