To me the main argument for decentralized wikis is when a community wants to capture deep subject focused knowledge. It's why I created https://wiki.osdev.org. Wikipedia is great but at it's core it will always be an Encyclopedia with a large breadth of knowledge. Specialization in a field is best handled elsewhere with links out from Wikipedia if possible. Especially when there will be original content.
Hyperlinking is all the decentralization you need in some cases. Activitypub for wikis is of interest for people contributing to a collection of specialized knowledge. No one is going to subscribe to all the specialized wikis of the world except maybe search/aggregation systems.
Wikipedia wants to be a specific thing with a specific scope. Where that line should be is debatable, but it will eventually be drawn somewhere. No matter where you draw it, someone will be on the other side of it.
However, mediawiki is open source. The licenses of content are cc-by-sa (similar to gpl). You can start your own wiki. Similarly licensed content can be moved back and forth if rules change.
Perhaps this is just manual "federation" in a sense, but the ecosystem supports it. I persinally believe this is one of the reasons why mediawiki as an open source project should be a core part of Wikimedia's mission.
When people disagree about content, Wikipedia always falls back to just reflecting what reliable sources says. And if they disagree, people can always collaborate to try to give due weight to both viewpoints.
But if there are no reputable sources that have already written about the subject, articles risk becoming someone's personal blog about their favorite topic. The notability criteria isn't a bar about what's important enough or 'deserves' a Wikipedia page, it's a super practical matter about verifiability, content disputes, and generally just being on solid ground if any claim is challenged.
* keeping at least minimum quality standards
* avoiding abuse by storing your files disguised as some "knowledge". At some scale the organization is not able to check even for a trivial instance of abuse.
* abuse legal problems by publishing illegal content (again, nobody will be able to do even basic checks if there's no limit)
* if anything goes, you get limited by physical needs like storage
> If you must, layer curation of what is notable on top of that.
Wikipedia is the curation. Store the non-curated data elsewhere.
