I created a simple plugin I thought somebody might find useful at some point.

It allows for new streams to be created from outside of wowza.
In creation a callback_url is specified that returns the next track to play.

It allows you to keep the logic of what to play outside of wowza, easily updatable and created in the language of your choice.

Problems that have not been addressed yet are server restarts (for now just try to recreate the stream on a regular basis) and scaling to multiple machines (with lots of streams, you want to divide the streams between servers)

http://github.com/wgrids/wowza_external_playlists