[welterde]

There seems to be XACE/XSELinux, which seemingly exists in the mainline Xorg distro now. I wonder how the experience is with that?

In practice I think it doesn't see any adoption, since most people don't run with SELinux or even AppArmor on their desktop and none of the applications run isolated from each other, so it doesn't matter that they all have full access to the X11 server. And for actual security there is qubes, which solves both the application isolation and the X11 security issue.

[nolist_policy]

Eh even if you secure the X11 API itself, your isolated app (browsers absolutely sandbox and isolate themselves from the rest of the system) will still share memory and have a socket open to an 33 year old c codebase (XOrg).

[welterde]

Not sure having shared memory and socket open to N fresh and under active feature development c codebases is that much more conducive to security? (N since while many compositors use wlroots there is still enough rope to hang yourself). To be fair, unless there is a exploitable bug in wlroots/lower wayland code, the blast-radius will be a lot more limited than if one is found in Xserver.

I think the Qubes approach is the only one worth considering if one deeply cares about security.