It all depends on the workflow, if one mostly uses 1-2 apps fullscreen it can fly.
They might do that, but it's not that high on user's priorities by any long shot.
Phone/tablet use has surpassed desktop use, and most of it happens on the go, on the sofa, on the bus, on the restaurant, and in other such places where no displays and keyboards make much sense.
For a niche, yes, they would be great (writers working on the coffee shop typing on their iPhone etc) but not for any majority of people, and not for Apple to "reassert their dominance".
Apple has been thinking about something like this for a long time.
This is extremely cool. The problem is, nobody really needs that.
Given that, I think a giant screen running iOS is less than 4 years away. Related: I don't think macOS is long for this world.