When threads goes live there will be tens of millions of people with existing Meta user profiles entering it overnight. There are currently ~13M Mastodon users, most of which I'm sure are not really active. So depending on how federation into ActivtyPub is set up, it will be like Eternal September x 100. Their content will likely dwarf anything out in Mastodon land. And judging by what I see on Facebook and Instagram, I don't hold out high hopes for the quality of that content or the behaviour of those users.

I'm not worried about it really because I think the ethic of fediverse as such that they will be quickly de-federated. But it won't be fun along the way.