But this seems easy to automatically block, no? If a client is querying an unknown domain check for some Matrix related data in /.well-known/ and add it to the block list if there is. And since the servers are publicly advertising the port used you just need to periodically check the list of known matrix domains you are creating in the first step.

Russia is already doing DPI and blocking ESNI so that seems easy. A more widespread usage of ECH would help everyone, as is Signal advocating, but that’s not the case yet.