Matrix is a federated protocol, so you can have a different home server and still talk to the majority of the network. Whats most likely is that instances who object to the risk is just a banning of missisipi ip's. And then its up to the people there to find a way to get back in. Nostr is a protocol though, you can have stuff like ditto.pub which is more filtered (they have some kind of spam filter) and very peer to peer options over tor like amethyst. So if there is a desire for very regulated nostr sites and relays that would be possible and its up to them to allow outside relay connections or not. But if they don't it has no real value for them to use nostr to begin with other than the identity carrying over. Thankfully the big ones tend to just be open to other clients or allow adding additional relays you wish to post to.