@Edent I've been having thoughts on search for a LONG time (decades... https://drunkdna.livejournal.com/69280.html ... this is probably my favourite thing ever said about me ever online and I'm impressed it's still there!) and it's safe to say I am VERY pro-search, but also pro-consent and individuals having granular choices around privacy everywhere.
I think the ability to make private posts OR public posts from the same account already solves the biggest and clearest divide there, but further granularity is not a bad thing, though the more complex, the more daunting for many in trying to navigate using any new app or site. It's tricky.
While it's obvious that it's impossible to search /eberything/ (but Google sure used to do a good job a decade or two ago, and we still have the Wayback Engine...) I'm very interested to see how search develops in Fedi. I think hashtags are doing an ok job at making things discoverable by topic, and it's been interesting to see how different sites have tackled discoverability. You gave a really good overview in your post. Kudos!