I like this idea a lot, and pushed for json5 at a previous job, but I think there are a few snags:

- it's weird and unfamiliar, most people prefer plain JSON

- there are too many competing standards to choose from

- most existing tools just use plain JSON (sometimes with support for non-standard features, like tsconfig allowing trailing commas, but usually poorly documented and unreliable)

Much easier just to make the leap to .ts files, which are ergonomically better in almost every way anyway.