There’s already things the M chip series iPads can do that the A chip series can’t.
Meanwhile, the MacBook stays with the M chips.
OSX does not run on the iPad because it would give iPad users an escape from profitable "value add."
Most people think they would be bad because they haven't tried them.
There’ll be hardware compromises of course, but software should run fairly uniformly.
For example Elektron a company that makes synths has some software that runs on Macs and are porting it to iPad. They have it running in beta at conferences. It does audio/data/midi of sorts of USB. They have explicitly stated it will only work on M chips for some reason related to underlying OS limitations.
It’s also my understanding that apps in the App Store need to be explicitly enabled by developers for A & M series compatibility. So there’s something different enough to allow devs to disable / enable.
At most you can make apps available to iOS or iPadOS separately but you can’t restrict the store listing to any category of iPhone or iPad device.
You can list capabilities your device needs but what falls under those capabilities is at Apple’s discretion.
"Note AudioDriverKit is available on macOS for Intel and Apple Silicon devices, and on iPadOS for devices with an M-series processor."
Maybe they are idiots, maybe the docs are out of date, maybe theres alternate methods.. but it does seem at some point there was/is an A/M series software ability differences in iPad OS.
I was referring to your last paragraph about the supposed explicit compatibility settings in the App Store per hardware. That is not a thing. Your example is specifically a capability, and one that requires PCIe, therefore needs thunderbolt.
Apple themselves may gate those capabilities behind different product classes, but as a developer you cannot. That in turn makes it very difficult to know specifically why something isn’t supported.
For example you can connect DACs and controllers to non-M iPads https://support.focusrite.com/hc/en-gb/articles/360012532199...
There are also capabilities that diverge in other axes like newer A series chips support things where an M series doesn’t. Hardware raytracing was an example of that for a while. Or still is because there are different gens of M series chips for sale.