Author here for your vacuum tube questions...
I am imagining something like a vacuum florescent display but with logic instead of display elements.
I guess you could do a whole circuit on photo-etched or stamped sheet metal inside a glass envelope in a similar process that VFDs, although I don't know how you would implement cathode heating. It would be an interesting exercise to think where that could lead you, but I think modern VFDs date much later, when semiconductors already wholly replaced tubes in digital logic.
What fails in a tube is usually the heater filament, which is a wear part with a limited life. Where some (very) expensive tubes did go is to have replaceable heaters - so not more but less integration.
Fantastic deep dive as always, thanks for doing such stellar work!
On that note, any chance we might get a teardown/history of Cray architectures in the future? Specifically the Cray-1 and 2?
To throw a more serious challenge your way: How about a write-up on the original Frank Rosenblatt Perceptron? I know finding an original Mark-1 part would be close to impossible but it blows my mind that they were successfully doing real-time visual classification in 1957 with an electro-mechanical machine (potentiometers and motors) using a 20x20 "video" feed with some learning algorithm that was not based on backprop.
I suspect quite a few as other "modular" systems in the transistor era like the later IBM Standard Modular System and DEC Flip-Chips ended up with plethora of specialised modules, but I'd be interested if that growth had already begun in the tube era.