I realized today that I was wrong about Webkit.
A few months ago, I wrote a blog post arguing that we needed a simpler, more comprehensible browser implementation so that we could experiment with different ways of extending and improving the web. I've come around on this now; we don't need to reimplement WebKit to improve the web. I think our solution to the glacial rate of progress in the browser will be something that works from the top of the software stack down, and I think web components and the Extensible Web Manifesto really hit the nail on the head in addressing this. From the bottom of the stack, we have Servo, and the two initiatives will meet in the middle sooner rather than later.
I still feel like there's a place for a simpler implementation of the browser, but it's not as critical to progress as I'd initially thought.