Related to #2313075: Allow users to upload webp files in image fields
Since webp is becoming popular, it would be nice if contrib could change the supportedTypes of GDToolkit without needing the extend the class, or even better add support for WebP out of the box.
PS: PHP 5.5 has build in support for WebP and since PHP 5.4 will be abandoned somewhere in 2015, it might be easier to just add support for it.