Transaction revocation within transaction malleability via anyone-can-revoke hashlocks

In a discussion on the Lightning Network, user ZmnSCPxj suggests an idea for dealing with transaction revocation by using private revocation keys. Rusty Russell responds, acknowledging that while the issue of transaction revocation has been solved, ZmnSCPxj's idea may have different tradeoffs than what Lightning currently uses. He notes that if the revocation key is not publicized but sent only to the counterparty, it is effectively equivalent to the current technique. Trusted watchers can also know the revocation keys, which have a compact form and require minimal storage.