So... Nothing apart from some convoluted anecdote? If currently there's no password manager in existence that doesn't let you override the plaintext password e

So... Nothing apart from some convoluted anecdote? If currently there's no password manager in existence that doesn't let you override the plaintext password extraction / override feature, there's nothing to stop one being made. You could probably hook it in with a system level service which cryptographically signs them, too.