Hot take: closing registrations on this instance will have been the secret sauce needed to make federation really take off, and others should follow pattern. Lots of instances with limited registration numbers is a good thing for now.
@Gar I somewhat disagree. It seems to me that it doesn't make sense to have tons of different instances that serve the same purpose. What we need are for instances that serve a specific purpose to pop up over time. What I think would help the federation AND growth would be a way for people to migrate accounts across instances. I think that Motoma on Github said it best: https://github.com/tootsuite/mastodon/issues/177#issuecomment-291550258