For me personally to use any of these sites, it has to at a minimum be a place where one can learn and have stimulating conversation. Reddit was like that in 2008, and it stopped being that way when memes, marketers, and political correctness took over. HN is the only site of this style that I regularly frequent because the quality is relatively high. Without keeping a high quality bar, I don't see why anyone would care to use any of these sites unless there's enough of a differentiating factor, and I don't think fediverse is an attractive enough of a feature to attract any serious users long-term. I mean look at Mastodon - it peaked when Elon took over Twitter, but has just been in decline since then.
I built my own HN/Reddit alternative [1] with the sole mission of retaining a high standard of quality. Will it work? Doubtful without at a minimum getting the ball rolling seeding it with content, and marketing is not my forte or interest. But in any case I hope we'll see more competitors trying to build a "better" Reddit than attempt to replicate the cespool that is Reddit (outside a few high quality niche subreddits), that persists not due to any superiority but simply just from network effects at this point. We don't need more of the same, we can do better.