> Engelbart's demo itself must have been a very early, (the first?) large-scale, live demonstration of interactive computer technology.
Teletypes had been commercially available for decades, and minicomputers (PDP-8) for about four years. It seems glass terminals started appearing only a year before this demo, though.
Have you watched the demo? Or looked up what an Eidophor is? This is pretty much the invention of the 'computer demo in front of a big, live audience'. I have no idea what teletypes have to do with any of this.
Obviously I haven't been understanding what you're tring to say. From your most recent comment, I think you're saying that the groundbreaking thing was showing a computer screen through an eidophor in order to demonstrate its functions live before a large audience.
With this in mind, I will claim that the iPhone demonstration is similar in that it's the first case of a phone being connected to a big screen projector to demonstrate its functions live before a large audience.
Teletypes had been commercially available for decades, and minicomputers (PDP-8) for about four years. It seems glass terminals started appearing only a year before this demo, though.