It appears that Garry has indeed replaced the old wiki with a completely empty new instance, however, registration is disabled at the moment. The new wiki is currently located at http://wiki2.garrysmod.com. An ETA until it will be usable is not known to me at the moment.
The wiki is still down, and I have not seen an official posting as to why. Is there any chance someone knows when Garry will be bringing it back?
The cached versions are better than nothing, for sure, but they are irritating to navigate, and it’s hard to find the pages you already know about, let alone obtain information you have yet to see, hence the reason for my post.