1) I don't really understand this criticism - why would a bespoke milspec controller be any more likely to be around than a widely documented consumer controller?

Which do you think is easier to replace today, or get a manufacturer to remake: a model M from 1984, or a custom machine keyboard from 1984.

Hell, wind the back another 10 years - I worked in a hospital with a really old bit of kit. It was a Siemens EEG machine, and the keyboard was capacitive metal tabs. No travel at all - they simply registered when pressed by a finger but not other things (like a modern smartphone screen). I'd much rather dig up a common keyboard than one of those curios.