[TheOtherHobbes]

But there's minimal non-trivial shared core logic, because the apps live in a different user space and do different things with different end goals.

You can port a Mac DAW to iOS - e.g. Cubase to Cubasis - but it's no longer the same product. Most of the features that make the desktop version so useful in a professional context are lost in translation, because iOS doesn't have the resources to support them.

So what do you gain by trying to merge development, except extra work and possibly extra confusion.