Apple itself leaked many mystery products that are coming out relatively soon. The leaked product identifiers proximity to others give some clues, but not many.
An example of an Apple product identifier
An example of an Apple product identifier
The release candidate for macOS Tahoe 26.7 was a trove of information for unreleased products. References to product identifiers littered the build, including for some known-about items.
For example, there was sightings of J490 and J491, believed to be versions of the Home Hub. B525 is expected to be the next-generation HomePod mini, while J229 was a potential security camera.