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.
@SneakyMission It's akin to changing your email address currently, unfortch.
My advice is do it sooner than later, or wait and hope they later add some sort of identity management?
I am on vacation this week otherwise I'd be spinning up a new instance myself to see how easy it is / how much it'll cost me.