This is baked into the way DMs are done in the protocol currently.

It would be very simple to break the chain of associations by including a "use this key for next message" in the messages and then every new message to and fro uses new keys each hop.

It's not even difficult to make this work with an async protocol, but this is how I designed Indra to work, with additional multi-hop onions to enable hidden services. It only needs to have the clients cache a few of the last received messages in case somehow one doesn't get through, the user can retry with an old key. Yes there is probably a DoS vector in this to try and catch the IP addresses of origins to bypass this but that'ls why Nostr - and bitcoin, indeed LN also, are successful - they don't try to solve every problem in one protocol.

That's exactly what Victor is doing with his work here.

It's not "privacy invading" to let people know that the protocol has zero privacy, but exploiting it is. Even if it's to "protect" users. Better to spend that energy finding solutions for the protocol if you ask me.