I like the mainframe PC analogy but I think in this case we are running up against ergonomics. People's hands are not shrinking and our eyes aren't getting any better. More interface may get offloaded to audio/voice, but we are such visual creatures. Until we are beaming data directly into our eyes, I don't think we will abandon the palm-sized display-- maybe foldable one like paper, or a tattoo, or my shirt sleave, but something.