Upper bounds on per-user bandwidth would help. Though for significant messages, one still has sock-puppet accounts (or aggregates of like-minded individuals with copies of the source message pooling their resources). And, of course, upper bounds create knock-on restrictions (should the system be allowed to transmit public-domain large-volume data? A bandwidth limit blocks that "valid" use too).

It's fun to game-theory how such limits can be broken.

Who cares about piracy? It exists over HTTP, too, and in a far greater volume than a modern USENET-equivalent could ever hope to achieve, and it's not like ISPs need to be sucked up to anymore: they've already taken their ball and went home on this matter, proverbially-speaking.