There is also a Jira issue:
Getting issue details...STATUS
The entire discussion is based on the epic "JDF in the cloud"
Although JSON has little additional merit compared to XML, we can't keep our eyes closed and ignore JSON. We definitely neither want XJDF to be ignored (too old school; not JSON...), nor do we want variant translation dialects.
Disclaimer: This is not a decision to actually add JSON to XJDF 2.1 but rather a request for comments.