It will require at least one generation that grows up using touch screen input methods that effectively are just as efficient as the full-qwerty keyboard.

Right now such a thing is pretty limited. Swype is almost there (I'm guessing based on what I've seen/heard/read - I have only touched swype a couple of times and I have no idea how to use it right) - but it still requires looking at the screen. 8pen/qwop -type input methods have much higher potential in the very long term... Not sure when/how that will catch on though, and it's likely that by then more technology improvements will utterly oust that approach out in favor of something even better - I.E. electrotactile screens and the like, which, if perfected, would probably be equal to good qwerty keyboards. *Shrug*