Great project, @jpmens .
An easily dismissable feature idea for you;

As with curl and vault, it could be nice to serialize the contents of a file using the @ prefix.

Example:

$ jo -p authors=@AUTHORS
{
   "authors": "Jan-Piet Mens <jpmens@gmail.com>"
}

Currently I'm using cat, which is fine, honestly.

$ jo -p authors="$(cat AUTHORS)"