Why isn't fractional scaling supported from day 1? I mean if you're going to do dpi scaling in the first place, why in the world would you restrict it to whole numbers only? Is it some insane hardcoded hack or something?

Scaling with changing dpi is the easiest thing in the world. Anyone who has written a program with some kind of 'zoom' feature (be it a game, image editor, image viewer, etc) knows how easy it is.