> Plus it's likely only a short-lived interchange format, not something to be retained for a long period.
Absolutely.
There might be an argument that it's not easy on the eyes in the case it would be consumed by a pair of them. It's absolutely valid. Golang community has found a solution for that called logfmt, which I personally appreciate.
It's somewhat similar to JSON, but a lot easier on the eyes, so if logs go to the stdout of a docker container and are forwarded afterwards, you still can attach to the live container logs and actually understand something.
If it's for that reason, logfmt is possibly preferable and there is already a lot of standard tooling available for it.