Amazon is actually EXCELLENTLY positioned to build a cross-domain paywall, a distributed Spotify for the web. Bezos owns the Post and knows the space, they have tremendous mindshare among developers (so the actual paywall API would be trusted out of the gate, hell they could even throw around AWS discounts to incentivize the cost of integration), and they have a strong ability to negotiate: "no, you don't get your own terms because you think you're a big news site, you get paid at the same rates everyone else does, because we're the WalMart here and our word is law."

The only reason I can imagine they haven't done this already is that they're mired in endless bureaucratic debates about whether this should be bundled with Prime... -_-