Regarding future-proofing; I realize going with a newer device = greater future proofing. But how long do you folks anticipate an iPad Air 1 lasting if purchased now? Do you anticipate it being that much less "future-proofed" when more basic apps are used? (I realize even those at some point will be optimized for the most current technology.)
One of the things going for the A7 in the Air 1 is that it's a 64-bit processor, using the modern ARM instruction set.
Just as the switch to a 64-bit clean architecture in the Santa Rosa and later Core 2 Duo Macs allow them to still run 64-bit versions of OS X like Yosemite (as long as Apple wants to support them), something denied even to the Mac Pros of that era.
Apple has already set a deadline for apps to be compiled in 64-bit, so that will probably form the demarcation line and set the stage for non-64 devices to be cut off.
The Air 1 will probably still run slowly with iOS 10 or whatever, but it should still be capable of running it.