Back in 200X, a graduate student acquaintance of mine had, for a research project, written a browser extension which transparently (as I recall, GPG) encrypted your emails in Gmail to people and decrypted those from them. I recall how pleased he was demonstrating it to people, and how much smoother and simpler it was than integrating GPG manipulation in your separate mail client.

All that to say, this is something at least some people have thought would be useful for some time, and it's nice to see some people getting access to that functionality.

(Now work for Google, not on anything remotely related to Gmail, remarks are my own, etc etc.)