RFC: x11: Drop support for multi-head
The main reason to drop multi-head support is that it has been simply unmaintained for many many years. When implementing a feature, we don't even bother checking if multi-head is broken, KCMs don't handle multihead, window management features are written for Xinerama. KWin is optimized for Xinerama-like operation mode in general, which is provided out of the box.
If you use multihead for esoteric gpu stuff, consider using kwin_wayland!