The rendering backend and Javascript portion, absolutely. The total lines of code for all of Firefox (Gecko, Spidermonkey, etc) rivals the Linux kernel.
But I fail to see why we can't have a full-featured browser front-end that uses Webkit, V8, etc as libraries. We have a lot of these projects, but they are always very spartan on feature-set, portability, extensibility, etc. It's almost always a team of 1-5 hobbyists, instead of a serious team of full-time employees. At $30m per 1% of the market, there's a whole lot of money to be made.
Just make it look like a native app on each major OS (Windows, OSX, Linux, BSD), let me move all the toolbar buttons around, let me put my tabs where I want them, let me load my ad blocker and script injector, don't spy on me, don't pack it full of adware, and I'm a happy camper.