This is the first time I’m hearing about this feature and am interested. But I feel like it would be better to use a different password than your master for these higher security logins. The thought being that, if someone has access to your passwords, they likely have access to your master password as well, unless they had access to an already unlocked vault.
I feel like defederating is a good short term solution, but the events described with XMPP could have happened in any number of ways.
The real focus should be on how to make ActivityPub robust enough to prevent the events from the article from happening again.