Limit to specific category

Something I had been looking at a while back for another use case was adding a filter when the metabox is added which would allow returning false to it to prevent the metabox from being added. Something like this in MultiPostThumbnails::add_metabox():

if ( apply_filters( 'mpt_add_metabox', true, $post_type, $post ) ) {
// add_metabox code...
}

You could use the $post object passed in to determine if you want it displayed for that post.

Would this work?