Since it keeps coming up, here's what makes it a challenge to get a retina display into an iPad. The iPad 2 with the same resolution as the mini had a 25 Whr battery, the iPad 3 increased the battery to 43 Whr adding thickness because the retina display requires so much power to drive - denser pixels require more backlight and you're also moving four times as many which is why the iPad 3 had the A5X processor instead of the A5 the iPad 2 had. This produced a lot of heat. The A6X in the iPad 4 has reduced the heat somewhat but you're still looking at a lot of power. The A6 in the iPhone 5 isn't moving as many pixels and is in fact similar to the iPad mini as far as the number of pixels it moves.
So, the crux of the matter is the battery in the mini is smaller than the iPad 2 at 16.5 Whr and yet still gets the same 10 hours running time as the big iPads because there is a smaller backlight and the die shrunk A5 CPU which allow for the smaller size. Sticking a retina display in, even with a die shrink of the A6X would still need a brighter backlight so looking at the move from iPad 2 to iPad 3 as an example, you went from 25 Whr to 43 Whr, gaining thickness in the process. A mini with retina could be expected to need close to double the battery capacity for retina too so you're going to need to fit a 30 Whr battery in the case which means a thicker and significantly heavier mini.
The current mini is a marvel of miniaturisation and cost reduction, and that is why it isn't retina because to make it retina would require it to be substantially thicker, heavier, hotter and more costly at which point, why not just go for the full size iPad? Android devices are less constrained to screen resolutions so they can play with different sizes and ratios, but they pay the cost in app quality. The mini works perfectly with all iPad apps, and cost competitive with the android 7" tablets while actually having a better screen than the Nexus 7 for example.
So, the crux of the matter is the battery in the mini is smaller than the iPad 2 at 16.5 Whr and yet still gets the same 10 hours running time as the big iPads because there is a smaller backlight and the die shrunk A5 CPU which allow for the smaller size. Sticking a retina display in, even with a die shrink of the A6X would still need a brighter backlight so looking at the move from iPad 2 to iPad 3 as an example, you went from 25 Whr to 43 Whr, gaining thickness in the process. A mini with retina could be expected to need close to double the battery capacity for retina too so you're going to need to fit a 30 Whr battery in the case which means a thicker and significantly heavier mini.
The current mini is a marvel of miniaturisation and cost reduction, and that is why it isn't retina because to make it retina would require it to be substantially thicker, heavier, hotter and more costly at which point, why not just go for the full size iPad? Android devices are less constrained to screen resolutions so they can play with different sizes and ratios, but they pay the cost in app quality. The mini works perfectly with all iPad apps, and cost competitive with the android 7" tablets while actually having a better screen than the Nexus 7 for example.
