Apple doesn't think so, either.
So, sooner or later, somebody is going to come along and eat their lunch.
Well Samsung is the obvious candidate for integrating laptop, iPad and iPhone functionality. We’ll see. I don’t see it happening. There would be a market for such a device but not a big one.
I just think it is a Human Engineering issue. You need to scale screen size vs. keyboard size vs weight vs. functionality to match human need. But there is no magic point where you can get a one size fits all solution to that design problem.
Ak yourself: How big would this 3-way device be?
Microsoft integrated the PC and tablet into their Surface line. Fantastic product.