The idea of a plugin that replaces one browser’s rendering engine with another’s has been floating around for years.
This is the ultimate F.U. from Google to Microsoft. “We’re chewing away at Office, Windows in general, and now we’ll decide when IE gets new features.” Of course it’s also a shot over the bow of other browsers; lag behind Chrome feature-wise at your own risk.
Will this take off? There are, of course, hordes of IE users who can’t install plugins, and some who won’t, but web developers will be pushing this hard.