Another thought on this - Apple's push to state driven interfaces with SwiftUI would make it a lot easier, provided the Mac and iPad versions are structured in the same way.

Which they probably will be because there are maybe three development shops that will spend any time thinking about how to make their Mac interface better optimized for a destktop OS.

Still not saying this is a good idea, but it's an idea. Wouldn't be surprised if Apple were exploring it internally.