I think this has more to do with the SoC pipeline than any display.
Same here.
Apple has booked most of TSMC´s upcoming 20nm production capacity and I highly doubt that devices that can use that are ready for mass-market production by July-August. September at the earliest, maybe even close to October. Apple does custom-silicon and that is extremely hard to tape-out without any flaws that could bite them.
Therefore, Apple needs to use an A7X chip with current process technology first and the bigger iPad is the perfect device for it, because it mainly needs more performance (while not constraining battery time) than their current offering. Since they are reducing the complexity of the backlight, they also save on power. So this is perfectly doable with a new chip that is not using a cutting-edge process. Also, AFAIK they are not going to use IMGTec´s Rogue IP just yet (it is going to be a 5xxMP variant of some kind).
When can we expect Series6 Rogue silicon?
King-Smith: We've already got 10 licensees. Silicon is coming out in the second half. And you'll see some strong platforms coming out very shortly with Series5 with OpenGL and GPU compute too.
The Mini needs both a cutting-edge process to save as much battery as possible, because of the inclusion of the retina screen and it also needs to offer more performance than their current offering (for graphics especially, that´s a no-brainer because of the retina screen). That is pretty hard to accomplish, when you basically have such a small device and are even more constrained than on the bigger iPad.
Also, there is going to be an insane demand for the new Mini (I would bet every cent I have on it) and because of that sourcing a Mini retina screen should be difficult if you don´t have enough lead time.
Last, but not least, Apple is probably going to focus on the new iPhone and the Mini for the fall-winter, because these are the devices that most of their customers demand from them. And they want to be blown-away.