There won't be any Retina Mac anythings except for the Pro until AT LEAST Haswell drops.
Go use a retina Macbook Pro running on the integrated chipset. Let me tell you, it's no fun.
Works fine under ML with integrated, for what MBA is mostly used for. Web pages scroll smoothly, full screen transitions go smoothly. Sure, there's a hickup here and there when more overlayed things move around at the same time, but I don't think people using MBA would expect some kind of 60FPS perfection at all times out of their laptop. Battery life would be a bigger issue due to more/stronger backlight needed.
Anyway, I can sing some praises to MBPR. I installed Win7 on it, installed Alan wake, running it with everything maxed out in 720p on my TV through HDMI, and it's running at probably 40-60FPS all the time. I'm quite in an amazement. Oh yeah, I can even use the DS3 controller to play the game with motionjoy driver (wired only for now)
Under OSX which always lags behind Win7 in game performance, I tried running portal 2, and with everything maxed out it runs in 1080p at 40-60 FPS. HL2 EP2 is mostly solid 60FPS with those same settings. I'll try Portal 2 under Win 7 and I expect it to probably be rock solid 60. Also, 1920x1080 and even 1280x800 with some AA looks pretty damn great on this screen, despite being non-native resolution. I've never seen scaled game output look this good on any other display to be honest.