Hey Laurens,
I think I’ve figured out where the problem lies; the new interface of WordPress version 3.8 was already included into Kanso before WP 3.8 came out, and when it did, the widgets section conflicted in a couple of places – the Footer widget area is still there, yet it became unseeable as a result of a CSS overlap. In any case, please try this fix, please download the attached archive, unzip it, and upload the contained files into the theme folder (/wp-content/themes/Kanso) replacing the existing files. Please let me know if it fixes the issue!
Sincerely,
Andrii / Satori Studio