Uhh, no, it wouldn't, because chances are strong you'll screw something up. Whichever technology takes the current model and extends it gracefully but usefully will succeed in taking the web another step forward.
Chrome is a browser, you know. It's the current model, extended gracefully. It's even built on top of a current engine.
They're using the phrase "start from scratch" to explain their thought process, not what they actually built at the end of that process. And that's generally okay. You can use any method you want to figure out where you'd like to go, before you try to work out how to get there via small, continuous changes to the status quo.
Uhh, no, it wouldn't, because chances are strong you'll screw something up. Whichever technology takes the current model and extends it gracefully but usefully will succeed in taking the web another step forward.