But the leaders of the project seem willing to take pretty drastic measures to, and it's good to see "neutral" communities adopt Mastodon as their platform.
Considering the first time I even heard that was this very comment, I'd say they're doing pretty well on that front. Basically every nook and cranny of the Internet has had to shake similar associations at some point.
https://medium.com/@EthanZ/mastodon-is-big-in-japan-the-reas...
Numerous communities have decided to move off of Twitter and on to mastodon, including lgbtq folks, furries, sex workers, FOSS enthusiasts. My understanding is that on the most popular instances, there's active exclusion and de federating extremist content, and those things live on repurposed versions of the underlying Mastodon software but are not at all connected to the community.
That's largely what happened with Usenet, and seems to be well-in-process with email.
Mastodon is an implementation of the ActivityPub standard. I've been on the platform since 2017, five years now, and have watched it go through various teething and growing pains, including mutually-incompatible cultures (e.g., Japanese Lolicon vs. World, also attempts by Gab and similar groups to join, largely rejected). There are strengths, including instance-level controls over moderation and peering / federation. That's scaled acceptably to a few thousand instances, but would likely be stressed were the network to grow to even a small fraction of the world's largest social networks. Given a one-tier model (users -> instances -> network), 10^10 active participants and balancing users to instances would require on the order of 10^5 users per instance, and 10^5 instances --- which is to say, 10^5 peering relations.
Given that most present admins are managing their peering / blocking relationships in their heads with a very minimal configuration system, that scaling problem seems unlikely to succeed.
My suspicion is that more tiers of relationships will appear, effective a hub-and-spoke system, of members, instances, and hubs, with roughly 1,000 of each on average. (This gives you about 1 billion total participants.)
What a "hub" means, or does, and how it interacts ... raises interesting questions. Which are entirely unaddressed so far as I'm aware.
(Note that in meatspace, we typically have geographic aggregations of people -> cities -> counties/states/provinces -> countries, or fourt to five levels of aggregation. This gives, in theory, roughly 100 members within each category. Clearly that's very rough, with cities often having far more people, and counties / states / provinces frequently having far fewer cities than the model would suggest. A large country might have ~100 major cities (again, some more, some fewer), and there are, counting as a physicist does, about 100 countries in the world (195 per worldometers).)
I've been largely pretty happy with Mastodon. I'm under no illusion that its success is guaranteed, or that it is inherently resistant to abuse or misuse.
I'm not sure if it's only my experience, but at least half of the profiles I bump into have an LGBTQ flag or belong to some minorities (sometimes I suspect that I'm the only white straight guy there), and so far I haven't witnessed any episodes of intolerance that got way too familiar on Facebook and Twitter.
I think that the structure of the Fediverse in general facilitates inclusiveness and moderation and it prompts people to be "nicer". If you're an intolerant jerk or a fascist, expect yourself to be muted/blocked. If you run a whole instance of intolerant jerks, expect other instance admins to mute/block your instance.
Eventually, they'll still be able to vomit their intolerance or conspiracies with their buddies on their own instance, and maybe find a couple of like-minded instances to buddy with. But they'll be basically isolated from the rest of the Fediverse, because most of the people don't like to read that shit, and most of the other admins will filter out their content.
And that's the best of the two worlds: intolerants and bigots have the freedom of speech that they crave so much, but very few are willing to listen to what they say.
However, it could also be that things are like this because the Fediverse is still relatively small compared to the major social media. 3-5 million people isn't exactly small, but it's still three orders of magnitude smaller than Facebook. It's still a bit of a green field mostly populated by geeks, scientists, open-source enthusiasts and instances specifically dedicated to hobbies. Maybe we just need to make sure that it remains like this? Just in case, I won't share a sign up invite with my parents...
However, this is still a bit of theoretical talk. In practice, nowadays the solutions proposed for inter-instance discoverability (relays and user directories) are still immature. The former has no filtering criteria, it's prone to spam, and many relays come and go within days/weeks. The latter is still operating at very small scales, but it's promising.
I believe that with better curated relays and user directories we can have the best of the two worlds: decentralized small instances that are easy to curate and moderate, but also well connected and discoverable. I'm considering running my own relay with instances dedicated to science and tech, but even the software for relays isn't that stable yet...
But in both cases, Mastodon was just used because it was the most mature software, not because of its federation capabilities or even the user base culture. Gab barely was part of federation. At first, they were blocked. After, they got out by themselves. Truth Social is not even available outside of the US, much less federating with anything else.
You've succinctly described Twitter's 2023 roadmap