You can use distros like Arch or Debian as a base and install KDE to it as a desktop. Many distros based on Arch or Debian come with a desktop pre-installed. Like KDE. My favorite distro with KDE is Garuda KDE lite (it removes the visuals from regular Garuda). It uses Arch as a base, just like Steam OS and works well for me to game on. Steam OS for desktops is something I think will become popular once the official release from Valve comes.