That's a really interesting idea. A big selling point of SwiftUI has always been that the rendering of the view code adapts to the platform. If it could do so as the platform changes within the same hardware config…
If you're suggesting that when "docked" to a Magic Keyboard, the UI looks like macOS, and when undocked, it looks like iPadOS, I worry about the cognitive dissonance of everything changing appearance.
A more unified look/feel would require a lot more work.