True, but if encrypted, shouldn't be able to decrypt.

The hardest part would be client integration. I can easily right a script to spin up new relays with random endpoint.

But configuring a client to allow setting PMs to using only the revolving relays would be troublesome.

That said, you could probably bake in all the rotating relays behind a single proxy endpoint like with this https://github.com/Dolu89/nostr-proxy