Every aerodrome that I ever worked at had a signal lamp - whether literally an Aldis or not. For zero upkeep, just occasionally, they are useful - for communication with WIP, if not aircraft. They certainly did not go out with the ark and it is a blinkered view to suggest that they did. Pilots of "heavy jets" most certainly should know the meanings of light signals, which are enshrined in SERA in the case of Europe.
As regards the additional technology that is available with a digital control tower, there is no doubt that it might well be useful as an add-on in a proper (conventional) tower, but not exactly vital.
The one question that I see Nats avoiding - or perhaps I have missed it - is WHY? There has to be an ulterior motive, knowing them, and it certainly will not be to enhance the status or conditions for the controllers.
The one necessary HF still to be addressed is the injection of JetA1 and freshly mown grass into the air conditioning - oh, and a genuine enthusiasm for aircraft in tomorrow's controllers.
2 s