Upgrade the display ??
I'm a little surprised that you think not upgrading the retina display is a demonstration of Apple missing a trick. Got to ask you , have you actually used a retina 13" macbook pro ? well I can tell you that 2560x1600 pixels on a 13" inch screen is plenty, I have mine dialled back to 1920x1200 using SwitchResX . I'm not much fussed about the font smoothness, just wanted the real estate on a small device. The brightness and colours are perfect , if they changed a thing on the MBP display I'd be suspicious.