Julien's post briefly recaps the history of the X protocol and then more closely looks at the current X11 protocol. While X11 has been living for more than two decades, numerous extensions have been introduced since then (i.e. X Render) while parts of the X11 protocol have been lost (i.e. Zaphod mode) and other features like server-side fonts are no longer used. Over the course of time, various tool-kits and higher-level software has had to work around the shortcomings of X11, which adds another level of mess and complexity to the situation, which Julien also covers in his blog. Also covered is the lack of interest by GTK+ and Qt developers in targeting the XCB API where as Cairo being one of the few libraries that targets the X C Bindings and then Enlightenment's EFL only has an unmaintained port.
X12 could clean-up some of this mess, but this FreeDesktop.org developer thinks, "To me, it does not seem X12 will happen in the next decade neither." It's also possible that X12 could also never come, if the Wayland Display Server proves to be a success or some alternative solution emerges.
Julien's post that shares his thoughts and ramblings on the X protocol can be found on this page. You can share your thoughts on X11 or hopes for X's future in our forums.