There are already standalone Windows MR devices with 6dof. HoloLens has also had 6dof for years. Vive has a stand-alone 6dof as well, but it’s only in China so far.
Sorry, I was wrong about that. I was thinking of Lenovo Solo, but that is Google Daydream-based. However MR does not inherently require a detached PC. HoloLens is a PC.