Just to clarify - ArtRage 4 didn't actually do any high PPI scaling. It had the inbuilt ability to stretch the panels to a higher scale but all that did was a visual stretch, it didn't increase the pixel density of the images so would have resulted in blurred controls much the same as if you set Windows scaling to zoom in when using ArtRage 5 on higher PPI monitors.

The removal of the internal scaling system was reqiured as part of a shift to a procedural interface that should hopefully allow us to implement a HiDPI system in ArtRage.