There used to be an operating system called "V" that ran the "W window System".

en.wikipedia.org/wiki/V_(opera…

en.wikipedia.org/wiki/W_Window…

W was ported to #Unix at MIT and switched to an asynchronous protocol. It was renamed to "X".

XFree86 and Xorg are implementations of X version 11, or "X11".

If there would be an "X12", this is what it might look like:

x.org/wiki/Development/X12/

In case you're curious about Wayland and not "Y", it's because it already exists:

y-windows.org/faq.html

#linux