Interesting, I imagined that a client would listen for notes on these other pubkeys though, we can't be having gaps like we do for bitcoin wallets, it would be wasteful.

I think it is simpler to just randomly generate npubs so we don't have to detect reuse and we should put the npubs in a private list so the client can be direct about what notes it is searching for.

Also when searching, it shouldn't batch because that would be a privacy issue but conversely, you only leak this to your relays so maybe it isn't so bad.