First question: while I know Apple has skipped an A-series chip in the iPad lineup before, have they ever introduced a *new* A-series in the iPad first? My recollection is that the iPhone always introduces the latest A-series chip. Not that they couldn't change things up, but it seems less likely. Note that the A10x-based iPad was released in June 2017-- just a few months before the A11 was introduced in the iPhone X.
Given this, unless they go a 2 full years between releases, the iPad Pro is likely to end up with the A13x-- only a question of when.
(EDIT: Technically it seems Apple announced the iPad Pro in 2015 *before* the iPhone 6s, in the same September event. And it was available after the iPhone 6s... I guess what I'm thinking is that I don't see the A series cadence moving up for a spring/summer 2020 A14 launch, but who knows.)
I do suspect the iPad is getting some additional focus / effort as a segment of their business that has growth potential, which is the primary reason they might move to a yearly release cadence. Doesn't mean they need to -- the OS update might be enough to carry it into next spring. I'm just wish-casting because I want to see a spec bump this fall when I plan on buying