In my scenario I imagine the iPad customer as primarily getting their computing done on the tablet but having the option to use a larger screen for certain edge

In my scenario I imagine the iPad customer as primarily getting their computing done on the tablet but having the option to use a larger screen for certain edge cases (mostly to illustrate the increase in capability over time). I don't think tablets will completely subsume PCs and that PCs will have a role to play for people who actually need it. Having a separate OS designed for that interaction model will net an overall better experience without having to make compromises in some way.