What about TideSDK?
TideSDK has made pretty good progress on that front, by leveraging web tech. He could maybe save a heck of a lot of time by porting TideSDK to cocoa and then pushing that
http://www.gnustep.org/information/aboutGNUstep.html
I think my point still stands. He wants to bring cross-platform cocoa, partnering with an existing product might be a better way to do it