Like I said, anecdote alert. But I think that aside from computer professionals, many people can be more than suited by an ipad + tablet case. The number of edge cases where a laptop works but an ipad doesn't work keeps on shrinking.
Rumor mill says Apple will be updating the MacBook air to be a tablet/laptop hybrid, possibly like the set up I described. That would be cool!
I know this is Slashdot so this is a little against the group think but isn't what you described exactly what Microsoft is trying to do with the surface? They made 2 versions, one that is stripped down with great battery life that runs office and a web browser. Then another one that is for professionals that is a full fledged ultra book.
I have used a surface pro 2 and it was a pretty good laptop for data viewing, though I still like a real laptop for coding work. I can see it being the only computing device someone like my wife would ever need.
I think in the long run the tablet market will be squeezed out by phones taking away the bottom and laptops taking away the top. Because lets be honest an iPhone 6+ is a great personal Netflix viewer and a Surface Pro or Convertible Mac Book Air would be better than a tablet with a keyboard case.