I like this idea, but it has issues. Write access is restricted to whitelisted npubs. But who runs this relay? Who's in charge of it? It's technically still ruggable by the owner if you're using a single relay.
Discussion
Yeah that needs working out for sure, but broadcasting fixes that. Even to the extent that the conversation can continue without your knowledge with people you don't know.
maybe that's ok (in this case), if it's run by a community member there is public/social blame involved.
Backup relays with easy migration are also an option to mitigate this