The X11 primary selection buffer is an even better variant of that though. It allows single-shot copy&paste (meaning only one application can grab it) from the password manager to the target application and it tells the password manager the name of the application that grabbed it.

I think it shouldn't be too hard to hack in a dialog to password managers to confirm if the destination is correct before replying to the data request. But even without that one at least notices that a malicious/wrong application grabbed the password.