Wouldn't it be the other way around? The subscription explicitly ties the reward to the quality.
Imagine this: (1) The publisher starts writing quality content in order to gather as much subscribers as possible. (2) Th publisher gets a comfortable amount of subscribers. So it starts to wind down the content quality, thus reducing his costs. (3) Now the users aren't getting the quality they are paying for. (4) Maybe slowly, but surely the subscribers will cancel their subscriptions and ultimately lose their trust in the publication itself. (5) The world is balanced once again.
Now this last point is important, the relationship between the producer and the consumer is based on trust.
Good Content would be peer reviewed by its readers, like it happens here on HN, and those reviews would in return garant those contributing some discount or even reward.
We are so far away from that like earth from mars.