> It's not perfect though. ls had support, but it was removed for reasons

In specific:

https://svnweb.freebsd.org/base?view=revision&revision=32810...

> libxo imposes a large burden on system utilities. In the case of ls, that burden is difficult to justify -- any language that can interact with json output can use readdir(3) and stat(2).

Which rather misses the point of being able to use JSON in shell scripts.