@matrix good writeup.
devices vouching for each other (or, designating one or more "authority" devices for an account that are unlikely to be stolen) is something my friends and i have been dying for!
it seems like it would be a much better way to revoke a compromised device, too, vs. the described flow of contacting each person with whom you correspond and making sure they revoke your stolen device's key on each of their devices, vs. just revoking it yourself once at home...