Thank you for this great plugin. I'm very happy there (now) is a preference voting plugin for Moodle!
Currently, the plugin uses the Borda count method to determine the winner. While this method has its merits (simplicity being one of them), there are occasions where a different ranked voting method might be preferable.
Based on the ranking ballot the plugin already provides, I would like to suggest giving users a choice of ranked voting methods. An overall excellent and widely used alternative would be the Schulze method.