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The best you can get is something like DNS or email, which are "decentralized" in theory but quasi-centralized in practice.

Which is much better than other systems; "twitter but like email" is a reasonable goal.

You can get more decentralization than those services provide, but not without sacrificing usability and/or security.

One key to a successful decentralized system is not being able to spam with it; if someone learned how to spam using BGP or DNS we'd all be screwed.