A website like that would be very helpful. A lot of people I talk to think that unlisted gives more protection than it actually does (they're used to how it behaves on YouTube where it's harder to discover), don't realize that it's still likely to get indexed by Googe et al even if they haven't opted in to search engines (because their post may well appear in a thread by somebody who has opted in), don't understand the limited protection of blocking if authorized fetch isn't enabled, don't realized that RSS leaves everything open etc.

Yes, I think in terms of protecting data generally, not just from Meta but also data brokers, Google, and other data harvesters -- as well as stalkers. Meta's a concrete and timely example so it's a chance to focus attention and improve privacy protections, both for instances that don't federate and for instances that do. I agree that most (although not all) of the information Meta can get from federating they already can by scraping and they certainly could scrape (and quite possibly are already scraping) most if not all profiles and public and unlisted posts on most instances, and so could everybody else ... it's a great opportunity to make progress on this. https://privacy.thenexus.today/fediverse-threat-modeling-privacy-and-meta/ has more about how I look at it.

Specifically in terms of data that flows to Threads through federating that isn't otherwise easily scrapable today, three specific examples I know of are

• followers-only posts for people who have followers on Threads, or who have approve followers turned off
• some unlisted posts from people who have opted out of discovery and search engine indexing that aren't visible today (i.e. haven't been interacted with via a boost or reply by somebody who has opted in). it's very hard to predict how many of these there are; it's not just posts that are boosted by somebody who has followers on threads, it also relates to how replies are retrieved
• identifying information in replies to followers-only posts by people who have followers on Threads. This can flow to Threads even if the original poster has blocked Threads (because blocking information doesn't get inherited by replies)

That said this isn't based on a full analysis so there may well be other paths. As far as I know the draft privacy threat model I did last summer is the deepest dive - And the software is buggy enough in general that it wouldn't surprise me if there are paths that shouldn't exist.

In terms of concerns about tracking others have about federating ... like I say for most people this isn't the top concern. To the extent it is about data going to Threads, for a lot of people it's about consent and/or risk management, full stop. They do not want to give Meta or accounts on Threads easy access to data from their fediverse account, even if Meta can get it without consent now (and even if they have some other Meta accounts). There's also a lot of "well Eugen said it's all fine", and especially from techies a lot of "well they can scrape it all anyhow, whatever" and "everything is public anyhow on social networks".