That argument is only sound for as long as the screen is unwieldy. If you could wear a pair of glasses that magically converted your laptop into a stable, triple-screen workstation, it'd be a no-brainer to assert that it was useful in at least some circumstances -- working on planes, trains, automobiles now becomes more and more possible. If the tech then progressed to the point where you could do that from a phone, and not require a laptop, or even necessarily pulling the phone out of your pocket, then it seemed like a pretty powerful productivity feature _at least_ some of the time, and if executed well enough, it wouldn't shock me to see people giving up their laptops in the same way that many people don't bother having tower PC computers any more.