Stage Manager is a fully integrated experience that provides all-new windowing experience that is incredibly fast and responsive and allow users to run 8 apps simultaneously across iPad and an external display with up to 6K resolution. Delivering this experience with the immediacy users expect from iPad’s touch-first experience requires large internal memory, incredibly fast storage, and flexible external display I/O, all of which are delivered by iPads with the M1 chip.
A lot of folks with 2018 iPad Pros and 2020 iPad Airs are pretty upset about this move, especially given the fact that the Apple silicon DTK ran on an A12Z My guess is that the company just wasn’t happy with the performance of Stage Manager on those older iPads.
2022-06-13 Update: Craig Federighi has chimed in on this, in an interview with Matthew Panzarino:
“Building to M1 was critical as well,” says Federighi. “From the start, the iPad has always maintained this extremely high standard for responsiveness and interactivity. That directness of interaction in that every app can respond to every touch instantaneously, as if you are touching the real thing underneath the screen. And I think it’s hard sometimes for people to appreciate the technical constraints involved in achieving that.
“And as you add multiple apps into play, and large amounts of screen real estate, you have to make sure that any one of those apps can respond instantaneously to touch in a way that you don’t have that expectation with a desktop app. Indirect manipulation gives you some slack there, so it’s a different set of constraints.”
He also mentions that older iPads don’t have the horsepower to push external displays in the way Apple wants. The whole thing is worth a read.