Would it be possible to have you fediverse username connected to the blockchain so you could use it to associate with an instance? And if that instance closed, say, you could simply connect your blockchain based account identity to another instance?
Why would blockchain be necessary to do that? Honestly, 99% of the time blockchain is just a highly inefficient buzzword.
Usually there are better ways to achieve the same outcome, with the added bonus of not automatically attracting a cavalcade of Web3 con-artists and grifters.