A little bit of time perusing a step tablet will tell the tale: look a the difference between 0.1 OD and 0.2 OD, now look at the difference between 1.8 OD and 1.9 OD - it's just not the same visual difference although it is the same same density difference.
Now, if you had this "D-Stop feature" in a timer you would have to tell the timer just where you wanted the density incremented. The same density increment takes a different time increment depending where on the HD curve you are sitting. And of course, it varies again with the paper and the developing and toning.
I find, in my printing, that a grey scale 'step tablet' made at around 10 equal stop intervals from white to black (ie, the zone system tones for the paper and developer I am using) is a very useful thing to have at hand when deciding on print exposure. It also shows me what will happen to the highlights if I move the shadow tones and gives a quick indication of how much to burn and dodge. With the meter and timer the strip lets me make close to perfect prints on the first try without any test strips - the scale makes it much easier to see what I am asking for, because, unfortunately, the system gives me what I ask for and not what I want.
I think making zone-system/grey-scale 'step tablet' should be the first lesson in darkroom printing. Takes only a half hour to make, prevents a lifetime of pulled-out hair loss.