Wouldn't that need them to get the fu.ck domain itself? I have a feeling that is already used by someone else, but there currently isn't any website at that domain (doesn't mean it isnt used)
Activitypub makes it next to impossible to "move" an instance to a new domain.
Every post/comment/and user is uniquely identified using the domain. In the eyes of ActivityPub changing the domain just makes each of those things a completely new thing.
You can set up a new service at your new domain and potentially get most all your users to migrate but they'll be leaving behind their entire histories and as a "new" fediverse user they'll only be discoverable via the historical posts for as long as the original server is reachable.
Thats IMO one of the worst engineering decisions in the protocol, besides all the others, but this one (making identity depend on domains, meaning on third parties antithetical to decentralization) is... laughable. Who was responsible for it?
But, the theory goes, you're not supposed to be reliant on third parties as you should be in control of your own domain (or within a few degrees of the person who is).
Large instances are what are antithetical to decentralisation.
Of course, the reality of it is that, it just hasn't worked out like that.
Not sure how well this would actually work, but couldn't the admins "copy" the instance to the new domain and then initiate an account migration from the old to the new instance for every account? That should both push out the account transfer to all the other instances and preserve the post history as well.