This seems like the first step towards broadening the product line by price points, a la iPod. That might be coincidental. But this seems pretty straightforward to me. Leaving out the iPad mini for a moment, as that has an obvious differentiation, just looking at their "full size" (9.7" and up) lineup...
iPad:
--Not top-of-the-line tech, though still extremely capable, in exchange for price. This is the budget version.
iPad Pro:
--Top-of-the-line tech, higher prices.
It made sense to draw the line at the iPad Air 2: the A8X was the cutoff for the split-screen functions of iOS 9. So perhaps that was the point at which Apple said, "we want to make this functionality available to any iPad purchaser." So you put the least expensive processor that will accommodate that (A9, I guess). Trade off on the laminated screen to save money? Done. Perhaps use the lower-end Touch ID? Also done. Very good tradeoffs to keep the price down.
I don't look at this as targeting existing Air 2 owners. And perhaps a refurbished Air 2 is the better value...but those will only be around so long. Apple has maybe established its new lower-tier offering, and set an expectation: a model that meets a certain lower bar for functionality (in this case, split-screen and Touch ID), but economizes otherwise. I like this move, if this is in fact what's going on. I don't worry about a repeat of iPad 3 -> iPad 4. If the iPad Pros get updated shortly, those aren't the sort of device you'd be buying if you were considering this new iPad. They'll be significantly more expensive for significantly newer tech.
This makes upgrading my girlfriend's iPad 3 more realistic.