Agreed. And further, the longevity of larger interfaces is also a matter of the overall quality and feel of the UX: A phone sized interface will probably alway

Agreed. And further, the longevity of larger interfaces is also a matter of the overall quality and feel of the UX: A phone sized interface will probably always feel constricting and confining when trying to tackle anything complicated. (And a good part of mobile UX is preventing and alleviating this feeling of claustrophobia, IMO.) It's extraordinarily difficult to cram the full neuro-kinesthetic experience of a complex task into a playing card sized screen; we're more comfortable interacting with things that are "body sized". But whatever the backend is (and remember, your users don't give a hoot where the computing is done), certainly large sized interfaces are not going to disappear. What is most likely going on is a re-centering of the bell curve: more people will have a smaller screen as their primary interface to the net/web, and larger interfaces will accommodate more complex behaviors and tasks as well as group activities.