There is a serious problem in this proposal: they want to disallow all keys not on a whitelist, and that whitelist does not include letters. Which would mean no WASD movement. While the intent is good (prevent phishing), I think a better solution is still needed.
Chrome has this and I truly and completely hate the way Youtube uses it. The only reason I switched to HTML5 video on YT was the fact that it resized to the browser window, therefore not wasting massive amounts of screen estate on my 24" monitor. The way I'd use it was to have the video on 2/3 of the screen and Vim on the other 1/3.
Alas, those days are gone, unless I figure out a way to override requestFullscreen to always return false.
> A Web application can’t arbitrarily make an element fullscreen without user intervention—the operation has to be initiated by a user action.
As the article says, the intent is mostly to offer similar functionality as e.g. Youtube's fullscreen mode. It's much simpler/cleaner to ask ordinary users to click a button on the screen (that is a part of your own interface) than to ask them to press F11. Also, F11-fullscreen doesn't stretch elements as this does:
> It allows Web applications to toggle the browser into full-screen mode and stretch a single page element so that it fills the user’s display.
Another reason might be that some browsers, for example the Firefox I'm running right now on linux, don't go into 100% fullscreen like chrome does. In my browser, it just removes all of the browser's interface except the URL bar and tabs.
I hate that Chrome has modified the fullscreen support so that it is no longer possible to have "fullscreen", mean "fullwindow" mode. It was my absolute favorite. Tiling WM or even manual, along with "fullwindow" mode was the best of all worlds. You were an F11 away from fullscreen, but had the flexibility of having just the video in a window to do with what you pleased.
