Apparently IGZO screens are potentially easier to make in higher pixel densities. If Sharp (or someone else) gets that working on mass production lines soon, then I suspect that will be the technology Apple use.
The iPad rumours pointed towards the device getting thicker because IGZO wasn't useable in time. The possible thinness of IGZO points the finger more towards the Air being able to use it, but I still think the top end Pro machines will still get the top end screens first.