I’m loving the HiDPI mode on my 3440x1440 screen.
I can now see everything clearly at a distance without having to squint at the screen. Much more relaxing.
Unfortunately it makes most third-party plugins much smaller and therefore harder to see, but I guess that is the fault of the plugins not Nuendo.
The latest Steinberg and Fabfilter plugins work well, but UAD, Eventide and others don’t have scalable UI’s at the moment.
It needs at least a 150% mode option as well. 
For me, 200% mode is way way too big.
OK. I’ve abandoned HiDPI mode - Nuendo looks good with Windows scaling set to 150%, but this makes most plugins look too small.
A better setting for me is HiDPI unchecked, my main screen (3440x1440) set to 200% scaling and the other two screens (1280x1024) set to 125% and 150% respectively. This makes everything large and clear, and gives me options as to where to place individual plugins.
You can utilize the built-in magnifier in Windows 10. Its hotkey is pretty easy to use.
That doesn’t work too well for me.