I think the OSX and iOS approach with @2x and @3x is the only sane way to go and is genius in its simplicity. It really works out well even for old apps that aren't updated (just double), while Windows' crazy DPI slider never worked properly. And you mention WPF, which for the longest had crazy blurring artifacts even in its text rendering.

People often say "just use SVG/PDF/vectors for all the things" but look online and you'll find many good arguments against it, not least because icons and text at lower pixel sizes really needs to be "pixeled" manually to look good.