Sure, but if you don't have instance reputation as a stand-in for user reputation, then you are back to ground zero on the spam problem and sybil problem. This

Sure, but if you don't have instance reputation as a stand-in for user reputation, then you are back to ground zero on the spam problem and sybil problem. This is not solved anymore than Bitcoin or Hashcash (anti-spam tool) it was based upon, or any more than email spam was in the 90s, or usenet spam in the 80s. Every time I've brought up that content federation and identity federation aren't the same thing and that having centralized IDPs handle the burden of keeping spammers out of the network, people chime in with "yeah, and don't limit me to google and facebook!" and kind of miss the whole point. Centralized is one of the few solutions to the spam problem, it's worked with email for example. The other ways are some kind of a reputation web (finicky and gameable) or to force people to put down cold hard cash (proof of stake/proof of work). This is all intimately tied up with crypto and spam because this same problem hasn't been solved for 30+ years and keeps popping up over and over again. Reputation networks are hard. (and, you can do identity federation without actually melding your content with theirs, and that in fact melding content into a global namespace isn't inherently desirable. There there may be cases where you want to do something different with the "domain"/"subreddit" than another instance, or what most other people are doing with that domain/subreddit - reddit "technology" is not the same thing as 4chan "technology" even though these boards share a discriminator, it's not even the same culture or style of discussion even if they shared a mechanical format.) But yes generally speaking the real problem here is there's like 10 different factions that all want to solve slightly different use-cases. Some people want self-hosted reddit, some people want self-hosted reddit with global boards, some people want explicit networking to specific instances, some people want something much closer to the decentralized/single-person instance with individual custom IDPs, etc. Nobody even agrees what they want to build.