I had to read the email I got about this several times because it didn't seem to make sense. Hang on, my New York Times subscription is going to end in September and then... that's it? The Kindle is wonderful for reading newspapers on, and now - what? And why? I'm sure that someone has a very good reason for the change. I'm also sure that I've never seen a deprecation so poorly communicated.
This is very bad for big periodicals with many subscribers. Under the current model, they get a predictable amount of income and are motivated by keeping the bar high for their content, lest they lose subscribers. Under the new model, their income is entirely based on how many people pick up that issue and read it, which makes it very hard to budget. It also likely means an inevitable slide into "politician SLAMMED other politican, and you'll NEVER BELIEVE what happened next" headlines, since extra clicks are very directly your periodical's source of income.
This is very good news for Amazon because it gives them far more bargaining power against publishers. Right now, if The New York Times decides that Amazon's terms favor Amazon too strongly, the Times walks, and Amazon doesn't get any more money from Times subscribers. Under this system, if the Times walks because Amazon terms favor Amazon too strongly, Amazon keeps the subscribers.
This is moderately good news for customers who read a bunch of stuff on Amazon Unlimited. You now get to read whatever you like for probably around the same cost, and the stuff you naturally choose to read will end up getting a bit of money from it. Yay.
This is probably moderately good news for niche, popcorn periodicals. If you have a "Werewolf Romance Weekly Short Fiction" magazine or "DIY Productivity Tip Of the Week" newsletter, you'll quite possibly make way more money by attracting idly browsing Amazon Unlimited customers than you would have been able to if you had needed to convince people to subscribe to your service.