There are some things about the iPad Air 3 which we can be fairly confident about. For one thing it's likely to run iOS 10, though iOS 9 is always possible if it arrives sooner rather than later.
iOS 9 brings improvements to Siri and Apple Maps, true multitasking for iPads, a new keyboard and more. So look forward to all that on the iPad Air 3 at a minimum. If it has iOS 10 that's sure to bring even more new features, but what form they'll take remains to be seen.
Another change we might see is a larger screen. Apple's all about making sure that users get the best out of the tablets they buy, and with the ability to run multiple apps on a screen, more space to do so would be welcomed.