It's dissappearance has likely to do with how FS/Z came to be. The entire story can be found in this thread (
viewtopic.php?f=1&t=32246), but admittedly it is rather long.
The TL;DR comes down to this: the file system was designed by someone from these forums, and had some (depending on your interpretation) fairly severe issues. The subsequent discussion derailed rather spectacularly, resulting in a (temporary, not sure here) ban of the original poster. My guess is (this isn't backed up by information in the aforementioned thread) is that somebody has since decided that the FS/Z file system was, given the issues, not worth having on the wiki, hence it's removal.
That said, it also means that FS/Z might not be the best choice for a first file system. If you do decide to use it, make a decision on solid arguments beyond just the advertised intent of the original author. In particular, it might be useful to at least understand where the criticisms given in the thread above come from, even if you don't agree with them.