We (Sugar Labs) are serving a lot of files with custom MIME types. Mirrors with missing MIME type configuration for these files are causing quite a bit of trouble, especially since most users don't understand what's going on.
It would be great if MirrorBrain could check the Content-Type for all files via HTTP
a) during the initial scan for enabling the mirror (mb scan -e <mirror name>) and
b) on a periodical basis (but not as often as other checks).