More power too em. V8 is a kick-ass js engine, but doesn't muck with the language. As long as they didn't take liberties with specifications (LIKE THEY DO NOW!) I would hope that they compete to render faster. IE9 believe it or not has the fastest canvas redraw and its not from writing a better canvas, they mainly just throw more horsepower at it.
This would actually give the W3C some legitimacy instead of being the internet's U.N.