The main reason people use Fandom in the first place is the free hosting. Whether you use MediaWiki or any other wiki software, paying for the server resources to host your own instance and taking the time to manage it is still a tall hurdle for many communities. There already are plenty of MediaWiki instances for specific interests that aren't affected by Fandom's problems.

Even so, federation tends to foster a culture of more self-hosting and less centralization, encouraging more people who have the means to host to do so, though I'm not sure how applicable that effect would be to wikis.