Currently the MIME database (include/mime.xml) is a static list provided as part of JAS. It would be handy if this list could easily be updated via the backend.  The question that comes to mind however is whether upgrade should overwrite a customized version. It seems rather annoying if you spend time to add your own MIME types that are subsequently forgotten when JAS is upgraded. Maybe adding a flag "custom" to the XML file to indicate it shouldn't be touched by upgrades.