I'm not sure Apple will do it, but I'd like it if they did. I'm really enjoying my Pro, it's the best iPad there is in terms of viewing and creating content, for sure. The big screen makes a huge difference. BUT, the size of the Air is still workable, and I think is ultimately the sweet spot for portability/usability. The Pro is just big enough that it's not as easy to just slip in and out of bags and use anytime, anywhere. I wouldn't pull the Pro out on a crowded train or heck, even bringing it to a meeting seems like overkill sometimes. I mean, on its own it's not big and it feels much lighter than you expect, but I've been using an Air so long I'm still kind of used to and prefer that size.
I'm keeping my Pro, but if an Air 3 comes out and supports Pencil, I would definitely pick one up and maybe downgrade to a base level Pro for home use only. Almost everything is a better experience on the Pro's screen, but I just find myself missing the size of the Air as a major part of the iPad's value proposition.