Good points. I would guess that for something to be implemented, it would have to be easy for browsers and API tools to check once per domain and cache the response and should probably be something that already exists and has been adopted. Maybe a page could have a meta tag or header that contains a hash of the destination sites DANE signature? Something like "targetref:somedomain.tld expectsig:39726a2fe2bb052cf00e6b95a8385f7" based on tools like danecheck [1] or maybe DNSSEC but that is very poorly adopted.