Im not sure I understand... Dynamic scaling is available in most software. The windows 10 scaling is quite frankly, terrible, understandably, because it was only recently just added to windows 10 and has to use "intuitive" guesses to figure out how to scale correctly.
You mentioned that this was not a problem when people were running on 1080p displays, which is also, just not true. The UI in Vienna's software appears to be built around when people were running 800 by 600 displays. I didnt do an actual pixel count, but, I have a dual monitor setup, one is a standard 1680 by 1080 display (22 inches) and the UI comes nowhere close to extending across the entire display on that monitor either.
Instead of discussing legacy reasons for why this problem exists, lets discuss why, in 2018, music software continues to have this problem and more importantly, how we as an industry can make music software more accessible. As a side note, I would venture to guess that the problem stems from the fact that music software developers are busy trying to check the next box on the feature list, and UI scaling isnt high on the list of checkboxes. In point of fact, accessibility options have always been low on the priority list for software across the board and I think this is a shame.
I dont know what programming language vienna software is written in, however, most modern programming environments have UI scaling builtin, if the programmer takes the time to account for it.
I would also argue that if I have to use the operating system to fix a display issue specifically related to one program, or a group of programs that all fall under one category (music editing, photo editing, video editing, web browsers, etc), that industry might have a problem that it should strongly consider looking into.
This is not just a problem with Vienna, this is a problem across the board. East West, Kontakt, and Cubase, all software suites I have in my workflow, have this issue. As music software gets more complicated, more buttons and fiddly bits are crammed into the UI until eventually, the little 5x5 pixel icon is shrunk down even smaller and a tooltip has to be added. I kid you not, some of the fiddly bits in this software contain more than 100 controls in a single paged incidence of UI, which appears to have a screen resoultion of 800x600.
When a person buys a 50 inch TV to use as a display monitor, they arent doing it because they want the UI elements to stay the size they are on a 22 inch monitor. They are doing it because they want things to be bigger... Music software developers dont seem to care about this however, and that is unfortunate.