The first thing you’ll notice in the image below is that there appears to be a cutout for the Smart Connector. Apple first introduced this connection with the iPad Pro, using it for a more stable and reliable connection for things like keyboards. This case leak suggests that Apple plans to add the Smart Connector to the iPad Air lineup with the March revision.
Another change is that the camera cutout on the back of the case appears to extend further down, perhaps hinting that the iPad Air 3 will gain support for rear camera flash, a feature the iPad Pro does not have. Finally, the leaked images appear to show holes for four speakers, a change that was first reported earlier this month.
With more power efficient internals, Apple could go with a smaller battery to make room for the speakers. If I recall correctly, I already got more than 12-13 hours of battery life from my iPad Air 2, hence they should have room to manoeuvre.