I think the vast majority of people will stay where they land, as they won't see the need to move elsewhere if it all just works. They come with the mindset of the centralised internet.
Do we really want those flagship servers to become the Instagram, Facebook, Twitter, etc. of the Fediverse? More than they effectively are already?
The biggest obstacle is not the problem of not knowing what an instance or a server is, and/or how to choose one.
The real issue at hand is that people feel they cannot leave their legacy platforms, for the very simple reason that everyone they know is on those platforms. It's the one thing I always run into: "But I don't know anyone on Pixelfed; all my friends are on Instagram, so who would I post to?", and "I only have Snikket because of you, I literally don't know anyone else on it. Can't you just be on WhatsApp?".
No tech solution or "Sigh up with Apple" can overcome that obstacle. It's 𝗛𝗨𝗚𝗘.
People resist change, and actively so. They will only move if they see a tangible benefit, and 'privacy', 'no tracking' etc. are not seen as benefits. In my experience people just don't care, and if they do, they don't care enough to do something about it. The network effect is real, and #BigTech knows it.
@Mastodon