The fundamental issue with decentralization is the challenge of decentralized information governance. This can be summarized by the idea that there's no cost to making a statement.
However, there is a solution: Reputation.
Reputation addresses the issue of cost without involving money.
I believe that without a Decentralized Web of Trust Reputation (DWoTR) system, an open decentralized social media or wiki platform will never achieve critical mass.
Until DWoTR is implemented, a decentralized wiki remains a futile endeavor.