Polishing the crystal ball
I agree with Marc that there are still some pieces missing from the Cocoon web applications puzzle, mainly regarding the backend. I've already stated that for me business code has to be written in java, as independent from the front-end framework as possible, to be testable and long-lived.
So what are the options for the business objects layer? Currently in Cocoon very few I think, and that might be a Good Thing as we might not want to write the business layer of our apps inside Cocoon, but rather outside of it, with a clean interface, either REST-like HTTP/XML, RMI, or Avalon components if we're careful about decoupling.
With my team we have started using hibernate recently for object persistence and we're very happy with it. Now what's needed is a clean way to interface such backends with a Cocoon frontend. Too many options, that's often the problem these days...