I could attach a debugger to the X server, however, debugging the X server pauses it, which would be a problem if I was debugging from inside that X session. Beside that, window destruction happens quite often, which can be prohibitive for manual debugging. It's still possible with a remote ssh connection, and gdb scripting, but it's inconvenient.

I will definitely look into eBPF and uprobe mentioned in the article, I don't know about them. But wouldn't something like XNest (or XWayland?) help with debugging X? You'd debug an X server running in a window comfortably from your real environment and display server without it being disrupted by the debugging session.