Back in March and April I wrote couple of blogposts about upcoming new great feature – full SQL/JSON.
Unfortunately, as of today SQL/JSON has been reverted (removed from sources), both from development version 16, but also from “almost ready" version 15.
There is lengthy discussion about it which you can definitely read if you're so inclined (side note, I didn't catch it immediately, so for future me – RMT is Release Management Team.
Obviously the feature will make its comeback. Whether it will be in 16 or later – can't tell now, but it will definitely reappear.
SQL/JSON is coming back, hopefully for PG16: https://commitfest.postgresql.org/41/4086/