Gmail won't implement most of these features, due to the classic innovator's dilemma. Too many people use and expect Gmail to work like a regular email app, chronological stack of emails with read and unread, so even though these features may help the more productive users, Gmail can't alienate most of its other users.

What they could do is create another email app, which they did called Inbox, but then they killed it and most of its features, which were similar to Hey's, haven't been incorporated, precisely due to the reasons above.