@ben There have been several opt-in attempts to do this as well. Those were driven off precisely because of disagreements over what constituted opt-in - many argued that the combo Eugen proposed for Mastodon 4.2 (and since changed due to feedback) would be sufficient: if a profile is discoverable (= visible to Federated timeline) and the toot is public, it could be indexed.
Crucially, third party projects could do no better, because that was the only metadata available. Mastodon 4.2 adds a new profile attribute (but sadly does not deprecate the old one - so privacy settings are increasingly oblique).