The chances that the next iPad mini will have a Retina Display?
In my opinion, not that high.
I hear a lot of people calling a Retina for the mini "inevitable," but I'm not sure as to why.
For one, 2048 x 1536 on an 8 inch screen just isn't necessary. I don't know who thinks the display on the mini is deplorable. I already think that the 8 inch model is superior for most tasks as is.
Second, think about how that will affect the justification for buying a new 10 inch iPad: an extra $170 for something with a battery that'll take almost 3x longer to charge but lasts exactly the same. THEN add in the fact that it will also have a lower ppi?
And how big would that battery have to be to support 10 hours of battery life on the mini? If the same as the larger iPad, it would make the mini feel like a tank to carry around with you, which sort of misses the point of the mini in the first place.