What do you have in mind? We can upload any docs to blossom and sign a note with the URL
Discussion
Whatever we could already do in PGP.
Given a signature and a message, get pubkey.
Given a message and a privatekey, get a signature
At this point, this would be enough for me 😛 points if I can just do it with a browser extension or amber.
this is similar to swap https://github.com/vstabile/nips/blob/atomic-signature-swaps/XX.md