I mentioned cappuccino and sproutcore in other replies here. Sproutcore looks interesting, and there's a great team behind it!

I mentioned GWT. As you know, it's Java that compiles to JS.

I don't see how YUI is different from jQuery and plugins. I don't see a router or templates in the yui docs.

Sencha targets mobile.

You asked what's missing. Well, none of them are based around jQuery, arguably the reigning king of minimalist js libs. Minimalism means less learning, easier to use. They are all pretty heavy. I imagine making something more like web.py or Flask or weby, but for frontend JS.

YUI3 is more of a framework than a complete solution, but personally I prefer it that way. It offers more flexibility.

Here's a post on defining your template within the html itself using yui3. http://lostsyntax.net/posts/5

I will admit I had a little trouble with that approach, and ended up defining my "templates" as strings within the javascript itself for unscatter.com. That's how the paging works for javascript enabled clients.

If you are really after MVC, from what I've read of them I think SproutCore probably comes the closest.

I think though, you need to consider the environment you're working in. Programming a system that will run on a server is much different that programming an application that will run on a personal computer, laptop or even mobile device. You're generally bound to a single core with limited memory availability. Syntactic sugar leading to faster development time is generally a good compromise on the server side, but on the front end you have to be careful. This warning isn't an attempt to disuade you from the existing frameworks listed, or even to keep you from writing your own. It's just meant to advise you of something to keep in mind while you do your application development. Know your box, and excel inside it.

Vaadin is not a client-side framework; it's a server-side Java framework that takes care of client-side code as well. It's similar to Nitrogen for Erlang.