The exact example you're describing is what the ActivityPub spec and the resulting "Fediverse" are aiming to solve. Mastodon and compatible microblogging platforms are distributed versions of Twitter, Lemmy & Kbin are compatible distributed versions of Reddit/HN style link aggregators.
Given the boost both of these parts of the fediverse have gotten from Twitter/Reddit's series of missteps recently, they're starting to look like they could become viable long-term alternatives.
Given the boost both of these parts of the fediverse have gotten from Twitter/Reddit's series of missteps recently, they're starting to look like they could become viable long-term alternatives.