Why? The iPad Air 2 is a beast...we should be very happy if the mini 4 is a smaller ipad air 2 with the same price of ipad mini 3. I'm going to try to explain this...
The iPad mini 2 was a really big challenge for Apple. They had to design a screen with same pixel quantity that ipad Air, in 7.9". So the pixel density is much higher. But the battery space of the ipad mini is tiny compared with the ipad air's space. Because of that, apple had to use an izgo display(with worse colour gamut) and an a7 chip with lower speed. And they have to increase the price to 389 from 329 of the original mini. They've needed two years selling ipad mini 2 and ipad mini 3(only touch id implementation and same screen one year later, so much higher benefit margin) to recover the big amount of money that they spent to develop ipad mini retina. Now, it's time to release a new version, but the challenge is bigger, because if they want to introduce a design with same thickness to ipad air 2, the battery space is lower again. So, if they could release an ipad mini 4 with the same factor of the ipad air 2, with same laminated display technology with perfect colour gamut and and antireflective coating, same power and graphics(tweaked a8 with 2gb ram and better graphics or a9, because a8x is too power hungry, like i said in older posts) than ipad air 2, same battery and same 389 price...
It would be perfect!!!