I am now a strong advocate that all free relays should delete all non-metadata content (not kind 0, 3 and 10002) after 90 days.
Most users not only seem fine with it but don't really care about saving their notes at all. They are here for the moment and not to build a database of posts they can look back on. Those who are here to build content are already paying for relays.
Then all free relays should offer a paid option that simply keeps all posts for as long as the user pays. Relays can use the NOTIFY spec to warn users they are about to delete some of their stuff.