I can't wait for ReactOS to become mature.
100% backward compatibility with all legacy and current win32 apps and games, driver compatibility with legacy hardware, able to dual/multi boot or live boot from a CD or USB drive.
And for old times' sake, a sprinkling of old Windows sounds, icons, themes (e.g. Microsoft Plus! for Windows 95), classic boot screens, wallpapers.
And Classic Solitaire and Minesweeper, and other bundled Windows games. None of the app store DLC crap.
In other words, ReactOS is to Windows what DOSBox is to DOS. An emulator, running programs natively or near-native, without messing around with virtualisation.