Context for posterity:
We're not going to continue with book callouts (booklinks) in this format because it doesn't meet our doc standards for maintainability or style. In the future we'll find a better way to gather and present related resources in the docs :)
These were all I could find with a cursory search, let me know if you know of any others! After this, we should remove the unused custom template code (https://github.com/raspberrypi/documentation/pull/3040).
Context for posterity: We're not going to continue with book callouts (booklinks) in this format because it doesn't meet our doc standards for maintainability or style. In the future we'll find a better way to gather and present related resources in the docs :)