Apple is now requiring app developers to use their recently added API for review prompts and is no longer going to allow custom options. This means that developers cannot create their own prompts to ask users to leave a review, nor control how often and when they appear. From the App Store Review Guidelines:

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.

This guideline change is good for two reasons and is part of a wider change to how reviews are going to work. First, it'll put a stop to apps that practically beg for a review every time they're updated. Second, a consistent user experience that allows for in-app reviews is going to make it much easier for users to leave a review, eliminating the need to nag in the first place.

Ryan Christoffel at MacStories shares what might be a concern among developers:

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.

Ask yourself this: how many apps have you actually reviewed? If you're honest, I bet that number is low. The annoyance of review prompts is largely because of the hoops that users have had to jump through to actually leave a review. This compels most developers to repeatedly ask for reviews, especially when reviews were hidden when a new version of the app was released, because many users simply won't bother.

I think the loss of control is a good thing for everyone involved. The trade-off is that the new prompt allows users to leave a review directly within the app. This is giving developers exactly what they want: a frictionless way for users to leave reviews.