oh, going the other way?
i've mentioned this before but not actually put it to a proposal
needs a new tag, i think "s" makes sense, and it would be formatted thus:
`["s","
or something like that
the PGP can't really sign correctly for nostr authentication though, that's a whole other can of worms
i've talked about this idea before, but the thing is that verifiers have to support the signature verification so it really needs to be added to a NIP if you want to enable it to replace the BIP-340 signatures outright
i'm pretty sure adding a new signature algorithm isn't that hard to do for gpg... but i don't know what's involved exactly
i would think it shouldn't be that much harder than creating helpers for git
but anyway, you are the C expert, this is part of the reason why i never got into C programming... it is a very brittle and hard to extend language