The facebooks of today make it effectively impossible to self-curate attention. Social media is the publishers early internauts tried to get away from.
I disagree with your last paragraph, though. The "old web" was a small walled garden. The "post slop" web is going to be very similar small walled garden, that is chased to get away from uninspiring everyday.
Here's a free idea for anyone hoping to launch anything like this: implement a MLM style transitive web of trust. The forum is invite-only. x strikes - you are out, but the strikes on invitees transitively decay over the invitation chain. If you invite someone who then invites all the normies who get striked out - eventually that strikes you out too. Invite yourself to shitpost - eventually you will get punished for that. Yes, it's bad as it can exacerbate bubbles as much as the current facebooks do. Simple updoot mechanism suffers from brigading, but something can be worked out.