I fear such a service may simply tread the same path as Wikia.

Also, any hosting platform has to balance user control over extensions and customisations, on the one hand, with system reliability on the other. You can't easily delegate control of extension installation to Wiki administrators, unless you give them console access.

The Minecraft Wiki is currently hosted by Weird Gloop which is the entity responsible for the forked RuneScape Wikis, and they manage the servers directly: https://weirdgloop.org/

The harder bit is convincing people to move, and trying to beat Fandom on Google. One of the reasons they picked Weird Gloop is the experience in this space - they've pretty much won the battle in respect of the RuneScape Wikis, which have sat dormant for years.

I'm not sure how much they automate the forking, but a number of these already exist and were contendors for recieving the Minecraft wiki.

https://wiki.gg is probably the biggest, but there's also https://abxy.org and https://weirdgloop.org/, who is now hosting the minecraft wiki