it reminds me, that would be a neat thing, a service you pay a little rent like $2/month and your personal local relay has a custom wireguard style VPN client that uses your nsec for its encryption. i'm pretty sure p256 keys at least (secp256r1) already can be used and 99.99999% of valid secret keys for secp256k1 are valid for p256. this would simplify configuration a lot. you configure the relay with your nsec and the VPN endpoint and you get a username.example.com subdomain.
i could build something like this to add to realy in a matter of a week or less. in fact, i already have a http reverse proxy that could be extended to add a user database that fetches from the service's relays to configure npub->name using nip-05 and that username would also be your subdomain. just probably need to have round-robin DNS to run multiple endpoints and configure the multiple endpoints in the relay and it would switch to another one if it couldn't reach the first option.
if only i had the resources to build this. i do hope i don't get stuck without a serious job prospect by the end of next month, i'm gonna be in a pickle.