This looks very promising nostr:npub1l2vyh47mk2p0qlsku7hg0vn29faehy9hy34ygaclpn66ukqp3afqutajft. 

Something like this would need to be deployed with a fully functional key rotation system. If somesite.com gets owned we are in a world of pain. 

But overall, I think you might be onto something big here for the normie onboarding use case. Of course the advanced option where people hold their keys directly always needs to be present.