The RAM increase is nice, a big reason why my iPad Pro feels so powerful is that apps stay in memory for such a long time. You can return to 3D games days later and they will still be frozen, ready for instantaneous resume. I would bet against the iPad Air getting a 4K screen though. For practical reasons, Apple would almost certainly pixel-double to get to 4K, for a resolution of 4096x3072. Those pixels would show a 4K video natively … but that’s about it. It doesn’t really add anything else, the iPad already has a great Retina display. Quadrupling the resolution would just result in a significant, unnecessary, hit on GPU and CPU performance to gain an almost-imperceptible improvement in display quality for users.
Neither of these improvements will reverse the course of the iPad sales decline, however. Besides 16 GB storage, tech specs are not the reason people aren’t buying iPads anymore. That responsibility lies in the software, with iOS 9 and iOS 9.3 (for education) displaying encouraging progress in this area.
You could argue that well-specced iPads are slowing iPad sales with many customers happily contented with the performance characteristics of older iPads. This isn’t a criticism — long-term customer satisfaction is preferable. I would be very upset if Apple ever holds back on its SoCs to artificially shorten the viable lifetime of a product.