it seems to me like nostr should switch to pkdns for relay names, and that wouldn't be a breaking change
No Nostr can't do anything like PKDNS unless they break everything and intentionally switch to this instead of the current key-scheme.
https://medium.com/pubky/public-key-domains-censorship-resistance-explained-33d0333e6123
Discussion
The relays themselves would be more censorship-resistant, but that wouldn't extend to Nostr users.