That's kind of my point, ten years is not a long time for machines like the ZNA, in 20 years time when it gets to a level where a well heeled hobbyist could afford one it could well be near impossible to find a compatible screen.
i feel like you are talking about me, although my heel is probably just as good as yours. i recently acquired a 16 years old Lecroy SDA6000A scope, try find similar spec to that in new market today, we could have half of our lung broken, and thats just a scope. a VNA however is much much severe, the older models are still not within the reach, unless you want to gather pieces across universe at a span of time and assemble them at home, with hope there will be some service manual still downloadable or help from knowledgable knowing about the stuff forum members. but few points about that old scope:
1) i currently trying to replace the screen due to some defect, its minor and still perfectly usable, i just need some perfection
if its just for small money, why not? i can keep it as spare part in case the new replacement LCD break in the next 20 years time. the touch panel on it is still in perfect condition. there are quite a number of options available in ebay, some look original and expensive, some are cheap no name brand. i bought and got the cheaper version of the lcd monitor, tested good but just to figure out the original working touch panel is stuck to the original defected monitor, so i have the cheaper touch panel ordered as well waiting for it to arrive. not much difficulty there.
2) there are few threads talking about upgrading older models to the latest HW and OS. so availability is not a problem as long as the technology still exist. obsolete technology such as CRT however, will make your point valid,on much much older models. but there are also threads talking about repairing those obsolete technology.
3) by coincidence, the LCD monitor used for the Lecroy scope is also compatible with much older Tektronix TLA714 LA, so its also applicable to other brand, that was once cutting edge, and technology still used today. moreover, i've added touch screen to the LA, something that wasnt speced during the production.
4) trying to make all Windows touch button of the Lecroy scope features into push buttons on the panel, i believe the panel will occupy a big chunk of your wall, there are so much buttons in Windows that needs conversion to real world push button. even if they managed to group them into logical order, i guess it will be several deep down the tree of push button menu. pressing buttons too many times can sometime unproductive.
5) if on urgent circumtances that the touch screen fails, while waiting for replacement part, we use the mouse connected through the back panel
I'm willing to bet that pushbutton switches will still be available in 30 years time though.
Although inevitably not the ones that fit the footprint used, or more likely, it's a membrane panel, look at how much late-90s HP kit goes bad due to that.
True and membrane panels are the work of a minor demon from a lesser circle of hell, the touchscreen panels are considerably more complex and I'd guess the one on that ZNA is 'context' sensitive, I.E. the 'buttons' change according to mode...
in contrary, i also got older Advantest SA, no touch screen. the lettering on the push buttons (i mean that plastics keys) are washed out. trying to get the same push buttons panels for the model is what we call impossible or unobtanium. unless we buy another SA with good condition push panel, but that can cost much more than the price i got my Advantest SA. if you put your bet on the no touch screen SA when it was produced, you are guaranteed to lose today.
i guess what you are asking is similar to China self made naked PCB with LCD and few push (mechanical) buttons on the side that sounds like a typewriter, thats sold many in ebay, including my ADF4355 RF generator. replacable yes, but if thats what you are asking, then our tools today will looks like the tools of the 60's, ymmv.