why have you not looked at Adobe Lightroom? It uses a simple directory structure that stores files locally in a standard file format (DNG). These days, meta for image files are stored in the file itself or XMP. No need for the complication of JSON.

Digital Negative (DNG) is a patented, open, non-free lossless raw image format written by Adobe used for digital photography.

The Extensible Metadata Platform (XMP) is an ISO standard, originally created by Adobe Systems Inc., for the creation, processing and interchange of standardized and custom metadata for digital documents and data sets.

Perhaps this why Apple and Google abandoned the market. The problem has already been solved. This why professional photographers use the software.