Nice thing about X was that it would talk to remote displays. I still remember sitting in the Pentagon demonstrating that the Suntools screen lock wasn't particularly secure. Then there was NeWS. This was Gosling's first attempt at a deployable language. However PostScript (even with Owen Densmore's class extensions), while a reasonable intermediary language is really sucky to actually develop. Java was a bit more refined. Of course, lots of things either implement X under the native window system or backdoor X with local extensions. We got around doing high frame rate image work on X via the SharedMemoryExtension and the ability to flip buffers on the retrace interval (both extensions, but commonly implemented by many servers).