From "Amazon now has a ‘Get book’ button in its iOS Kindle app" on theverge.com:

Apple has appealed the decision, but is also complying with it in the interim, prompting several companies to announce app updates making it easier for users to pay for subscriptions and services. That now includes Amazon’s iOS Kindle app. Contrary to prior limitations, there is now a prominent orange “Get book” button on Kindle app’s book listings.

I just tried. It's there, and, though obviously easy in retrospect, the implementation surprised me:

Kindle iOS kicked me to Safari, which I keep in private mode, and the "Buy with one click" button is activated.

Okay, well shucks. Upon further review, apparently I don't usually pay much attention to that button, because it's always active, even if you're not logged in. Click it and it asks you to sign in.

But I wouldn't expect that to last long. Right now it looks like Amazon is only adding ref_=rekindleDP&nodl=0 to the URL, but they could add a unique, one-use GUID to the link and, with only a little risk to themselves (oh no! we gave away 200k worth of bytes to the wrong person!), make the button "live" immediately.

Adding a one-use, unique "buy now token" would make it easier to buy using Kindle than Apple's own Books. I click buy in Kindle, I click a "buy now!" button in the browser that's opened (no Touch or Face ID required), and a universal link sends me right back to Kindle.

And this would change our relationship with the web on our phones by merging apps and the web in ways I didn't really picture before. Now, Amazon knows where you were when you considered buying a book. They can do an okay job of fingerprinting you, not that they couldn't with you signed in within the app, but the extra data doesn't hurt. And, app review psychosis aside, there's no way for Apple to protect you beyond the way they protect any other surfer on Safari. (And with other default web browsers now on iOS, they can't always even do that.)

This is a pretty significant wall breaking down in the garden. I'm still tempted to think it's a huge positive for devs and users, but watching the platform regain its equilibrium will be fascinating.

That said, I feel like universal links are about to get overhauled.

Apple might soon say...

We'll let you out of iOS, but we're not letting you back in.

Ugh. Tim Apple strikes again.

(Though I haven't heard of them changing the rules there yet. You think Tim Apple's Apple (vs. Phil's Apple) would've had those universal link rule changes in the license already.)