Well, I'd imagine a 9.7" iPad without wide colour gamut and with only 1 GB RAM wouldn't be high up on the list for a pro/semi-pro Photoshop editing machine.
But then Apple released 12.9" iPads with 4 GB RAM, and then updated the line to include wide colour gamut. Also, at the same time competitors for the lower end like Affinity started popping up, too. And of course, the current iPad Pros actually are competitive in performance vs the MacBook Pros, with as much as 6 GB RAM.
I think the fact that the 3rd gen iPad Pro is paired with Photoshop mobile for the presentation makes a lot of sense, since Apple wants to highlight popular pro software and wants to market its latest hardware, and Adobe wants the most powerful iPads out there to make their software look as slick as possible.
However, that doesn't suggest in any way it would be limited to the Pros, and in fact there are 3rd party previews out there that test it on older equipment. The tests I've seen are still Pros, but are the 4 GB 2nd gen iPad Pros, which are actually a bit slower than the iPad Air 3 (which has a respectable 3 GB RAM).
Current builds of Photoshop run fine on iOS 12 apparently. I suppose it's possible Adobe could limit support of the final version of Photoshop to iOS 13 or later, meaning no 1 GB iPads would be supported. In this scenario, the minimum would likely be the iPad mini 4 (A8, 2 GB RAM) and iPad Air 2 (A8X, 2 GB RAM). It will be interesting if they release the final version on iOS 12 though, since iOS 12 supports a lot of 1 GB iPads. However, if they do release it on iOS 12, it's also possible they could just say that the iPad mini 2, iPad mini 3, and iPad Air are not supported.