The problem for Apple is that they defined Retina as "you can't see the pixels" and there is no need to go higher PPI than that. But the pixel doubled iPad min

The problem for Apple is that they defined Retina as "you can't see the pixels" and there is no need to go higher PPI than that. But the pixel doubled iPad mini would have a resolution higher than that. So they would need to spend battery life and processing power on something they have themselves stated is worthless. It's an odd situation.