Excuse me, but BS. At least for anything of actual relevance.
X11 networking works okay for stuff that looks like a classic X11 app. That's things like xcalc. Any modern text editor, web browser, or anything else is going to be dog slow.
X11 has a bad networking protocol that's way too latency sensitive, and as a result is nigh unusuable without something like NX, which puts a local cache in front to get rid of that latency.
No, I'd say X11 wasn't designed to be run on the network, in that no particular care seems to have been taken to deal with latency and bandwidth issues. It's more of a feature that could be had for free, because if you can use an UNIX socket, you can also use a TCP one with minimal work, so might as well allow it.