They're pushing GSuite for governments, corporations, schools... Things like 'read receipts', email recalls, and such are common questions and common scenarios that are supported by their competition. I bet this is in a well curated list of requests from schools, healthcare organisations, and MegaCorps alike...

For people outside the Google sphere there are numerous alternatives to make this appealing. A single-use link, for example, or just slapping OAuth on there. The baseline is open email, so any kind of trace-ability is a huge improvement.