A problem I’ve been considering recently is the tendency for decentralized systems to develop emergent centralization in response to non-adversarial conditions e.g. to improve scalability.
Federated systems/platforms suffer this issue so much I’d go as far to declare it systemic to federation general.
Email is a perfect example of an ostensibly decentralized, distributed system that, in defending itself from abuse and spam, became a highly centralized system revolving around a few major oligarchical organizations. The majority of email sent to today is likely to find itself being processed by the servers of one of these organizations.
From “On Emergent Centralization”