Well, by analogy with Rack, WSGI, Ring, Plack, etc, widget systems and forms and AJAX are way outside the scope of the problem that Clack is trying to solve.

All of these systems boil down to providing a simple convention for web applications to interface with web servers by implementing exactly one function that takes the environment and returns a triple of response code, content-type, and content.

Everything else you describe would be built on top of this, not built into this.

You've missed the point here, think framework-agnostic web server interface (like WSGI or Rack) rather than web framework (like Django or Rails).

The Weblocks developers could use Clack to interface to web servers like Nginx or Apache rather than maintain their own web server interfaces.

I use weblocks for small demos and private stuff, but at work it's all Clojure now.