We are nearly feature complete on our Cocoa framework. There are only a handful of controls left to do. Those on the beta list have been seeing our progress as we have released betas of previous releases (including R4). Once we are feature complete, we will start the final beta process, most likely within the next 30 days. At that point, we will take as long as is necessary to make sure the Cocoa framework is stable. And our plan is to ship the IDE based on Cocoa at the same time. The IDE is a large, complex project and is a good test case for the stability of the new Cocoa-based framework.
If you are interested in beta testing the new Cocoa-based framework, make sure you join the beta list. You can do so by signing into your account on our web site and clicking on the Beta Program link on the right side of the page.