I think this is a pretty poor reading of the market. Everyone has a phone. An increasing segment now has little access to desktop or laptop computing. I know I hate that I have to pick up my laptop to do relatively small tasks that I'm halfway through on my phone.

Offering a dockable screen/keyboard/mouse, using the phone battery/compute/storage seems like it would be trivial for Apple.

Obviously cannibalises laptop or tablet sales, but that's not the market's disinterest.