You can get pixel perfect scaling at any integer scale, not just powers of two.
Actually not true. There's currently a BYOND bug that causes certain hardware configurations to slip into linear interpolation.
I don't think that's a BYOND bug; I think it's a bug in those drivers. Although I'm not sure which you're referring to, exactly. Software rendering in DS and the map editor (the map editor doesn't use DirectX) is setting the stretch mode to HALFTONE which is basically linear rather than nearest-neighbor, so for those two it's deliberate. DirectX seems to do whatever the driver wants for its upscaling, and we have zero control over it.
There's a feature request in id:1388769 regarding the upscaling mode in hardware rendering, but I have yet to find any info at all on how to control that in a way that's compatible with our setup.
Actually not true. There's currently a BYOND bug that causes certain hardware configurations to slip into linear interpolation.