The line drawing width may also have to be adjusted in several places, for example the parameter editor and instrument editor. Maybe we could switch those to use GDI+ (it's implicitely requried by MFC in VS2010+ and comes pre-installed on XP and newer anyway) and have anti-aliased lines as a free bonus.

Starting from Windows 10 1607, there is SetThreadDpiAwarenessContext which we could use to selectively scale some plugin UIs but not others (probably not trivial to implement, though). When OpenMPT is not set to be DPI-aware, we should also consider using SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_UNAWARE_GDISCALED) as it will essentially cause fonts to be no longer blurry even when scaled up. There are a couple of remaining UI glitches (some random pixels at the top of pattern and instrument editor, and maybe more) that currently prevent us from using it, and then there is of course also all those plugins that will potentially also look broken for the same reasons.