Include users that follow users you follow? Any follower or following based metric that can balance between social network nature and spam protection?

DM unlock with sat payment might also work, though I just find the expensive identity approach unintuitive, at least I suggest to exhaust attention economy based ideas, eg. follower relationships, first.

Also, would you consider making the post text on top of the reply pane scrollable? Composing replies can become difficult if you can only see a fraction of any longer post you intend to reply to.