For decentralized social media to happen, there needs to be sufficient motive to leave centralized platforms collectively within a cohesive
network of individuals, so that if a tipping point is met to overcome activation costs, most of the network will move over so the new decentralized platform has similar value to the old centralized platform that the network was previously on. A few incentivized individuals in a wider network of apathetics won't work -- it needs to be a cohesive network all switching together in order for the value to remain competitive with the old platform, due to Metcalfe's law. And since we're talking about decentralization, the network transitioning will ideally be incentivized to choose a decentralized network to migrate to, vs another centralized one (even though the usability and quality of experience on the decentralized one is likely to be inferior.) This combination of factors is what makes it so difficult to bootstrap these networks.
Here's the thing: there is such an opportunity now, if anyone is willing to take it. Conservatives in the US are outraged against perceived censorship and de-platforming by centralized social media platforms. Regardless of the validity, there's a deep seated hatred of these platforms forming and an incredible sense of urgency to move elsewhere. Since the motivation for leaving is overcoming centralized control, this audience is particularly attracted to accepting decentralized platforms. Given that approximately half of the US aligns partially with the views of some of these voices, this is a large potential network. The catch is that we are also living in an era where if someone develops and delivers such a solution for this market, they're going to be under vicious attack and be labelled as sympathizers to the extremist, minority voices of that audience. Most likely their careers will be destroyed by choosing to build for such an audience, regardless of how much the extremist voices are actually present on the decentralized platform.
I predict that if we are ever going to see a decentralized social media platform emerge for any of these services, it will begin with a critical mass of marginalized voices who have been censored and de-platformed, and their audience, moving to it. Instead of beginning as a "toy", it will begin as a "place for undesirables." Today that could mean conservative voices in the US, tomorrow it could mean something else. If the network is able to garner sufficient growth, over time, as it always goes, the nature of the "average user" will be diluted away so the network is no longer perceived as a community of like-minded individuals but instead as a general, global platform. (Similar how most mainstream global social network sites today began in a similar way: Twitter was for techies, Facebook was for college kids, etc.)
Look out for these leading edge behaviors, and don't just dismiss them if the early adopter audience has the perception of being unsavory to you. It seems somewhat inductive that, given the current existence of the global centralized platforms, any long-run successful decentralized platform likely could not start any other way than with groups of people who both want to leave collectively, and who will get no benefit from staying (in other words, the people on centralized platforms will all want them to leave too.)