The iPhone 6 does have a polarizer which helps tremendously in daylight, and fixes rainbow effect seen if you have polarized sunglasses (at least for me on Oakley Juliets, and Oakley Crosshair 2.0).
Hard to say what the actual changes will be though. From what we've seen I expect the iPad Mini to get lighter, and the iPad Air to get thinner. If they finally start optically bonding the screen to the glass that alone would help tremendously.
The hard part is that others have optically bonded screens to the glass, and other screen technologies. But Apple traditionally sells many times more units of their devices compared to say the Kindle Fire (higher color accuracy) or Surface (optically bonded at similar screen size).
I'd expect a thinner screen system for the iPad Mini leading to thinner design. I'd expect the iPad Air to possibly get optically with maybe a polarizer.
Important thing to remember is that the iPad Air is still about 50% lighter then tablets in it's class. Outside of refined bonding to the glass I don't think there is much they can do with the screen itself.