> It would be very interesting to see the old systems rewritten in a modern language, with modern engineering practices, but keeping the old UI and UX (which often is incredibly ergonomic) - so as to limit scope and not mess it all up by trying to introduce mouse navigation and windowing mess.

I was the tech lead on one of these projects. Personally I was sad and frustrated we had to keep the old UX/UI. I would have much rather have made something more ergonomic for our users. Alas retraining would have been too expensive to do that even though it would have been probably more intuitive.

I do agree with you that there is some benefit to being able to do everything on a keyboard without having to deal with the baggage of what we consider modern.