Earlier quoted context omitted.
Where did you get the 1000 high voltage transistors thing? I used PLATO at UIUC in the late 80s briefly, because they were still around, but everything had been WYSE-50 or Sun already (or contemporaries) and the PLATO terminals weren't some monstrosities....just looked 20 years old.
In the simplest case you need one transistor per row and one per column for bitmap displays. If any transistor in omitted, than that row or column must have a fixed voltage, which means that the corresponding column or row of pixels would no longer be controllable and they would display the same pixels as whatever other column or row is selected at a given instant. One thousand transistors do not need a huge space (t…
You can build a system to control a large binary system with simple relays and gates and a comparatively few transistors.
Given that they did much more work with relays back then, in absence of a better idea I would pin my bets on that.