26 drive letters? The NT kernel and NTFS/ReFS are very flexible, just update the WinAPI!
For some reason MS nowadays messes around with the UI (Win8/10 theming isn't that beautiful nor intuitive), the privacy settings, windows update, instead of keeping the Win9x/XP/Vista themes and improving the Win32 subsystem. Even WinRuntime API is a Win32 subsystem citizen. Either improve it or port WinRT to another subsystem. I wonder what Dave Cutler is working on at the moment (after VMS, WinNT kernel, XBox and Azure platform), or has he retired?