I don't. The tech isn't there to make it thin enough and maintain acceptable battery life at the same time. Battery tech and screen thickness are the limiting factors in this case, not GPU performance. The Intel HD4000 has really impressed me for onboard video. It can really push a lot of pixels.
I'd say Apple's desire to differentiate between the Air and Pro models is also a key factor.
Until Ultrabooks go "retina" there's really no reason for Apple to do it. Once they do, the gap between Air & Pro CPU/GPU will probably increase to become the key differentiator between the two lines.