But that's not HTML 5 per se, but a browser plugin. And we were doing that years ago wtih all sorts of browser gaming plugins. Someone writing a cross-platform engine that plugs into different browsers that allows hardware access is going to have to develop that per platform. You may as well use Unreal Engine 5 that's (hypothetically) developed with a version for every platform out there, then use Flash v12 in a PS4 browser running on a Sony developed Flash engine, as you'll get much better use of the system resources.Which both supports your statements and goes to show that development on web games are on-going. Adobe has shown a demo of a Flash 3D engine that seems to provide near Burnout Paradise graphics. The equipment it's running on was not mentioned...
It's also worth considering that by the time browsers can play COD, proper PC and console games at that perioid will be two generations beyond. Which sounds about right, browser games being comparable to some 16 bit titles, although the lack of hardware acceleration has held back browser based (read Flash plugin based, as they're not written in javascript on an HTML canvas) games so we haven't had acess to Amiga level games with 60fps smooth scrolling and many sprites.
All in all, browsers becoming an actual high-performance gaming base is both a long way off and relatively off topic, because AFAIK you can't write a full game beyond the basics in javascript running in a browser window (edit: clarify that for proper fast action games, and not puzzlers etc). Server based apps where the browser just shows a video feed are more OnLive! type technology, for discussing in that thread.