I regularly attained 13-14 hours of heavy usage on my iPad 4. Battery life was insane. Probably one of the reasons for the dramatic design change with the Air 1... to bring it back down into the 10 hour range.I'd take more battery life as well... The iPad 2 and 4 had great battery life, and the Air 1 and Air 2 went down hill - of course both get to 10 hours, but the iPad 2 could get to 20 hours and my sister still drags over 20 hours out of her iPad 4. I believe the Pro 9.7 is better than the iPad Air 2, but whether it matches the iPad 2 or iPad 4 is unknown to me..
The current 12.9 iPad Pro is a beast... performance-wise and size-wise. The glaring weak spot is the current state of iOS. I can't believe how easily I've been able to modify some of my workflows to be able to use it BETTER and MORE EFFICIENTLY than with my Macbook Air. But the more I rely on the iPP than on the MBA, the issues and limitations with iOS become more evident.
My irritation with it is growing... mostly of the "this thing is so close, come on Apple and seal the deal!" variety. I was disappointed by the lack of ANY announcements at WWDC of iPad-centric iOS enhancements.
TL;DR: Although there may need to be some additions (like 3D touch) to the hardware, the greater update need is software in general, iOS in particular.