I'm not sure that monetization has a huge amount to do with the story. Usenet was populated by hobby bloggers, and there are still a lot of hobby bloggers-- many of them are the same people, but there are plenty of new hobby bloggers showing up all the time.

I'm not convinced that most of the professional bloggers are better than the best hobby bloggers.

It's plausible that the unowned character of usenet couldn't be duplicated these days, especially considering that rather few people would settle for an ascii-only medium. On the other hand, Moore's Law might make a modern usenet feasible.

In any case, as you say, individual sites could have trn, and it could be combined very nicely with an rss feed to give that "page down through your favorite newsgroups" feeling.