Comment by mrktf

Digging deeper there are mechanisms for long time on internal X side (see https://www.x.org/releases/X11R7.6/doc/xorg-docs/specs/Xserv... ) - granted never seen it practically implemented.

And going to rabbit hole there are even proof of concept security implementation named Xnamespace for Xorg fork (needs polishing and much more patches but looks doable. see wip documentation: https://raw.githubusercontent.com/X11Libre/xserver/d2b60a3d6... )