I created a wiki to list the communities on Fandom. It's a long way from listing the 385,000+ communities hosted on Fandom, but with your help, we can make the most complete list of wikis ever! You can add your wiki or look up a wiki you might not have known about!
In agreement with Fandyllic you might want to set up at least minimal organization like wiki categories as per the WAM page TV, Games, Books, Comics, Lifestyle, Music, Movies and Anime. As well as making an infobox to be used on each page.
And maybe contact fandom for a list of active wikis if they can provide with a name, topic, type, etc. list for you to start with?
While the idea behind it isn't bad, it's incredibly difficult to actually maintain it. There have been previous attempts at with hubs, and there have been attempts to revive it in some way, things like this quickly come down to "once 1 person gets bored of it, or once it gets too much for 1 person, the project is quickly abandoned". Wikis come and go all the time, and for example the number of pages is quickly outdated. All the wikis should be listed on the global sitemap, but I agree with Fandyllic and Hollowness that it still lacks logical organization