There are not many sites I would pay for that are purely content. I think HN is one of the few that could get away with charging $5/month and not lose me as a r

There are not many sites I would pay for that are purely content. I think HN is one of the few that could get away with charging $5/month and not lose me as a reader. The biggest problem is that most sites can't transition from free to subscription without losing most of their customers. Even a site that proves to be extremely useful could not do that without a competitor popping up that'll offer the same service for free.