While I like the general thrust of that idea, there are some kinks to work out.

For example, suppose someone pays $/month for Cubic Zirconia Membership Tier on a site that boosts their posts over the hoi polloi.

That person makes a post hyping up their company or product with a link. Isn't that also a "paid advertisement", just with a different payment scheme? What happens if their product is a scam or otherwise legally-problematic? If gets Section 230 protection, how can we prevent sites/advertisers from abusing the new definition?