Just say you have a quite large and complicated desktop application written in objective-c/cocoa written properly in MVC. You then wish to replace the V and C so that it is
There is a new web development platform for Objective-C/Cocoa called Bombax. It sounds like exactly what you're looking for (it is designed to allow you to write entire web applications in Objective-C). Perhaps you could even combine it with Cappuccino. You can check it out at http://www.bombaxtic.com.