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https://www.an-yal.com/blog/mixi-2-the-revival-of-japans-social-media-pioneer Mixi 2 is a name which has come up lately.
It might also be a sign that Silicon Valley (and in the case of Mastodon, Berlin) are just not delivering. Federation is sold as a silver bullet for everything. Bluesky pretends to be decentralized.
I'd hope that "safe" isn't a synonym for being censorious here (the article mainly talks about minors being banned from the site rather than censoring content).