Way before that — the X window system.
He's talking about it working at the same level as a browser where it sees if you have HTML5, and if not falls back to flash, dynamically.
I can't imagine it being a high priority - fiddly, low return, creates huge performance issues. Lots of basic problems - you don't want someone supplying input to a game over a (latent) network. You don't want to be running instances of performance-intensive games on your webserver.
Still - the proposed idea is distinct from VNC or X.