Windows 9
It appears Windows 9 will support 8K displays. DailyTech

It has emerged through a leak that Microsoft's upcoming Windows 9 OS will support high resolution displays up to 8K (7680x4320), double that which windows 8.1 supports.

PCPortal has published a couple of screenshots from a build of Windows 9, which is said to be available for Microsoft partners. The screenshot shows the new size for the Windows Explorer icon in Windows 9; the other shows better scaling for classic apps to make use of higher DPI. The report further claims Windows 9 will support display resolution up to 8K.

Windows 8 has issues supporting devices with high DPI (Dots per Inch). With the Windows 8.1 update things became better.

Last year Microsoft introduced the DPI scaling improvements with the 4K display technology. The improvements focused on optimising the usability and readability of high DPI display, providing uniform experience on multi-display systems, and empowering developers to optimise app-specific scaling based on display DPI.

But the support for high-resolution display still does not bring any significant change on products from developers, as well as Microsoft, reports Neowin.

However, this will not be the similar case with the brand new Windows Threshold update (Windows 9), which will make an appearance via the Technical Preview version on 30 September. Windows 9 will support devices with double the resolution that Windows 8.1 offers.