In the spirit of "do one thing well", I'd so rather use this to construct JSON payloads to curl requests than the curl project's own "json part" proposal[1] under consideration.
Agree, I was surprised that the cURL feature was considered as it seems to go against the "Do One Thing" and composability points of the UNIX philosophy.
Curl does like 100 "things" already by that standard. The Unix philosophy doesn't have to be reductionist.
Curl does do one thing: make network requests. This feature is making it easier to make network requests, i.e. it makes it better at doing the one thing that it does.