nevermind.
I just did the calculation. at 326 ppi,and 960x640 of my iphone 4s, it works out to be about 12.8 pixel/mm
if we scale 12.8 pixel/mm to 2048x1536 resolution, the screen will be approximately 120mm wide and 160mm in height. the diagonal size is exactly 200mm, which works out to be 7.87 inches. exactly same as current size.
There you have it. If the next ipad mini will use retina, it will be taken from the iphone 4s/5 panels. The LED backlight just need to be longer which can be easily done, but LCD panels and the technology is straight from iphone 4, 4s, and 5 screens.
Why is it important? This also indicates a retina ipad Mini will have in cell touch, taken directly from iphone 5 and ipod touches, as it will use the same panels.
Is it possible pricewise? yes it is. its same screen is put in ipod touch 6th gen for 229. But i suspect Apple do not have a low enough powered chip that can power 2048x1536 yet (A5/A6 too slow, and A5X/A6x consumes too much battery for mini size battery).