@rra well, the Fediverse currently has a few million users. It's still kind of small. Currently you can not follow your friends on Instagram or twitter. If Threads federates and blocks your server, it's still like it is now, isn't it? So we don't loose anything really, or not?

I understand your concern, but it could also be the other way around. Currently your friends loose their contacts switching from Instagram to Pixelfed. If Thread federates they can switch to Mastodon without loosing them.