For some specific needs, I created a command line utility in Python to manipulate Kdenlive project files. Source code is available at: https://github.com/kdeldycke/kdenlive-tools . Feel free to send pull requests !

This script currently provides a way to list producers and replace instances of clips in all timelines, as a workaround for issue #1941(see: http://www.kdenlive.org/mantis/view.php?id=1941 ).