dtonon on Nostr: The problem is that it is not backward compatible for existing npubs. One solution ...

The problem is that it is not backward compatible for existing npubs.
One solution could be to use a NIP-32 tag signed with pow referring to the profile. This way, everyone can validate their own npub.
This also allows one to 'whitelist' someone else, for instance someone who has been invited to join Nostr, making onboarding easier and more pleasant.