On the #Vergecast @imdavidpierce said something like: On every #SocialNetwork 90% of the users read, 9% post a bit and 1% post almost everything.
This does sound right, and for #Mastodon, #Threads and #Bluesky it would mean, that they don't need to be connected fully.
If the top 10% posting on #Threads and #Bluesky federate/bridge, you can basically get all the content on #Mastodon & #Fediverse.
Maybe with a certain follower number you could get bridged auomatically, @snarfed.org? Could be a middle ground between all opt-in vs. all opt-out?