In iOS 10.3 earlier this year, Apple introduced a new API for prompting users to give apps an App Store review. At the time, developers were allowed to continue using any custom review prompts they had previously implemented, with the warning that such permission would eventually be revoked. As reported by 9to5Mac, that day has already come.
App Store policy has been updated to mandate use of Apple's standardized rating API going forward, disallowing custom review prompts. The updated language in Apple's review guidelines reads:
Use the provided API to prompt users to review your app; this functionality allows customers to provide an App Store rating and review without the inconvenience of leaving your app, and we will disallow custom review prompts.
In the few months since its introduction, adoption of Apple's review prompt API has been slow. Perhaps it is due to that lack of adoption that the company wasted little time before requiring its use.
Apple's solution certainly provides a better user experience than custom alternatives, particularly since it allows rating an app without needing to visit the App Store. But the concern from developers may be the loss of control over when, or how often, that prompt is presented.