One concern would be:

1. Say Lemmy/kbin grows organically to 1 million users.
2. Threads federates, with 100 million users

Do you want these users flooding Lemmy? I don't want to be biased at the theoretical type of user on Threads, though if the right wingers/trolls/extremists migrate to Threads because they think it's "more open" then that may be an issue. If it's full of soccer moms posting pictures of their kids, or karens complaining about everything, that may be an issue.

Multiculturalism is great, I want to hear new ideas, though some areas are breeding grounds for lower-think, it seems. This probably sounds prejudiced or elitist.

I want to talk to the vanguard people who take the risk and are openminded and come to lemmy, not necessarily the "lemmings" who join facebook because they love facebook and don't want to, or can't, delve deeper into why facebook is one of the worst forces in media at the moment.

I am not prejudiced (I hope) against "regular people" and "soccer moms", though think that if 10 million soccer moms came here, the discussions may not be as... interesting, as they are.

Also, I don't know what lemmy instances will think about downloading masses of data from threads.