nostr:npub1l2vyh47mk2p0qlsku7hg0vn29faehy9hy34ygaclpn66ukqp3afqutajft (who else) had one that I’m not sure was ever merged but is in use. It involves creating an event defining a future key you might need to rotate to and then open timestamping that event to “notarize” the time. 

I have some sort of odd mental block on remembering the number or the site on this one but I’m sure Pablo can fill in the blanks.