Felix Miata wrote:

> No way I'm going to bother with anything like that every time I switch
> displays. One of the reasons people use computers is to have things done
> automatically that otherwise would be difficult, awkward or even

but this is a setting that you make one time.
I think you don't understand completely how this works. I'm not sure my
understanding is correct, but let me share what I understand.
When you have a physical display lets say 21" diagonal. This gives you
particular dimensions. Look here
https://en.wikipedia.org/wiki/Display_size#Display_sizes_of_common_TVs_and_computer_monitors

And this also gives you a specific set of pixels supported. Changing DPI
changes how many pixels are involved in displaying whatever you want to
display.
On LCD display lower resolution is somehow poor, though everything looks
bigger.
To solve this I choose bigger icons and DPI 120 for the fonts.

> impossible. UIs, DEs and WP apps do the right thing with text by resizing
> automatically according to logical display density, as when a primary or
> only display is switched or otherwise replaced. Default themes should
> behave similarly, keeping icons appropriately proportionate to the
> accompanying text and surroundings rather than having arbitrarily selected
> bitmaps that take no account of display density or space actually
> available for them to fit into.

What you are talking here sounds nice in theory but in practice it looks
quite different. Example: I have a LCD (notebook) with 1366x768 and
external monitor 1920x1080.
In theory I could "clone" and have the same output on both, only I would see
it much smaller on the LCD. However our beloved Intel graphics do not
support this. You know there is some hardware part that must do the job in
practice. So what I can do is either base on 1366x768 or on 1920x1080. I
prefer the latter and do 
xrandr --output eDP1 --scale-from 1920x1080.

> 
> Most of this thread really has nothing to do with $SUBJECT, the goal of
> which is to be able to demonstrate impact of a difficult to verbalize
> configuration change to someone in a different room, building or
> continent. Since no one has made his interest in this thread known, I must
> assume at least for the time being it is a difficult or impossible to
> solve problem, but the question remains whether there is any point in
> registering a wishlist bug to someday have it solved.

Well it turns out that the subject is invalid as you (1)can not run this as
normal use, (2)you can not run it from within an X session and even if you
could, (3)you can not use it as you need a window manager, session manager
etc etc.

I hope this helps

regards