I seem to be the only one who doesn't want a thicker or heavier iPad. My iPad Air 2 is amazing the way it is. I would even like it to be a tad thinner and lighter. The speaker vibration doesn't bother me. I also get about the same battery life on my iPad Air 2 as my old iPad 3. Standby time isn't quite as good since the battery on the 3 is like twice the size of the Air 2, but I don't let my iPad sit for weeks at a time anyway.
Maybe it would be good for Apple to maintain the iPad Air and the iPad Pro 9.7 inch. The iPad Air could continue with the thinness and the Pro (mini) could prioritise battery, features etc over thinness thus meeting both needs