FYI, the iot package is now in “extra” packages of 6.48.3. From the change log:
*) package - added new “iot” package with Bluetooth (KNOT only) and MQTT publisher support;
For those that might be tripped up by this like I was, it seems that using the /iot mqtt publish command in scripts oddly requires the “test” permission.
Also, the toJson function from http://forum.mikrotik.com/t/fetch-http-data-how-to-send-properly-an-array/107696/1 combos with mqtt publish nicely.