Better display scaling
Windows 8.1 handles display scaling far better than previous versions of Windows, but the way the OS natively handles high-resolution monitors is still far from perfect. As laptop and desktop display resolutions expand, the desktop interface simply shrinks rather than scaling to fit the screen. Sure, it’s crisp. But, geez, it’s small.
While you can enlarge text and icons manually, it’s a pain, and some elements of Windows—not to mention numerous programs—just can’t be manually scaled. Scaling desktop elements on a 13-inch laptop with a high-res display quickly consumes your on-screen real estate, as well.
With ultra-high-res displays becoming more common and less expensive, it’s a problem Windows 9 needs to fix, pronto.