I've had MacBook pro 17 inchers for 5 years now. But this is what I want to upgrade to: iMac 27" retina with 16gb memory and desktop class processor. It'll beat the pants off my first gen i7 mbp.
The current iMac 27in display is already near to what most would call 'RETINA' and, if you look at what's happening in Korea, I don't see any large form factor LCD panels for sale - indeed, there is a big buzz about 100Hz refresh rates on the existing panels Apple use and costs for the panel itself are just over US$150 - me. I'd rather a 30in iMac based on present ISP screen with built in motion sensors based on Kinect and Leap Motion technology.