Every once in a while new file types get proposed on Commons (see for example https://commons.wikimedia.org/wiki/Commons:Village_pump#Stereoscopic_image_formats_support_.28.JPS_and_.MPO.29). We should document the technical requirements for a new file type. Think about for example the ability to render the thumbnail and security requirements. This makes it easier to evaluate new requests.
(if we already happen to have this somewhere, please paste the link and close this ticket)