giftwraps are probably the best solution but they are clunky
Discussion
they are not
NIP-42 is
if everyone ran their own relay
only use relays with NIP-42 enforcement for DMs, simple
the relay can already know your pubkey by linking it through your other REQs and your IP
you could also establish a key you use for DMs to a specific person and another to receive, and rotate this every so often
gift wraps are a client DoS vector and do nothing to actually obscure info from relays