Rewriting a web framework from the ground up is so often a trap made alluring by the illusion of repeated code. Could there be a more optimal way of writing UI code? Of course. But a lot of UI code should just be treated for what it is: largely unmaintainable and unextendable, especially in the face of design changes. I'd love to spend a weekend hacking out a sexy, interactive app, but I'm not yet willing to invest 2 years to save a couple days of redundant development. I'll leave that for the companies not worried about making money or do it on the side through an open source project.
Two people, six months - most of it discussion, ~40K C# code, in my previous job we had a framework, compiler, debugger, mini IDE, app server with a kind of tiny in-memory database (supported object-graph-style navigation) that let us write interactive UIs using databinding with minimal repeated or hacky code, and a whole bunch of other hard-to attain features (for example, application code version rollovers with old sessions running in parallel with new versions until they're finished with, without needing to restart any process or machine anywhere). I've seen it done - more than that, I've been part of doing it - and I have yet, in the intervening 4 years, to see anything as well suited to its purpose.
It's cheap and easy to be cynical about these kinds of things. But it's very important to realise that there is so much that is possible today, but will be dismissed by cynics, that tomorrow we'll say "sure, that was easy, anybody could have done it" - but very few did.
Anywho, cynics are useful- they make us reconsider the value proposition we are putting forward. However, an idea shouldn't be discarded just because a cynic addressed it :)