For me, the limitations of my 12.9 Pro are rooted in iOS not the hardware itself so I'm more interested in what iOS 11 brings than any new iPad hardware. In other words, if iOS 11 is nothing more than iOS 10 with an animated emoji pack, then it doesn't matter what the new hardware brings.
According to rumours Apple are looking at adding things like being able to annotate (with the Apple Pencil) within things like Safari, messages and other apps. They are also said to be looking at allowing people to hook up their iPad Pro to a Mac and kind of use it like a Wacom. Obviously this is only rumour.