Are you meaning it as they would just try to scrape all of the user info off all of the instances they can see or just for gather info from people that interact with their users?

If it’s the former, what would stop a company from setting up a private lemmy instance and start doing that for all other federated servers? Services like ChatGPT and Bard may already be doing that and we would not know.

If the latter, then I guess just don’t interact with those users?

If they cannot collect my personal info any more than any other Lemmy or KBin instance can, then honestly I don’t care. If they want to make it interoperable, ok good, I’m sure somebody will be happy. I will not be signing up for an account, and if I don’t go out looking for the content I may not ever even see it.