I've long been wanting to rank images in galleries, as can be done with cast.
This would be ideal. For episodes, I try to arrange them in order of events as depicted in the episode and it would be especially beneficial for the main show guides, as to segregate images based on season and/or photo shoot (although a gallery for seasons may help that problem a bit). I've tried to add them in order, but in addition to dealing with discovering new images after a gallery has been populated (and this goes especially for older shows where stills aren't easy to unearth), but the system occasionally goes screwy and cocks up the order I place them in.
If a rank was implemented, then a nice touch would be for stills that are of deleted/alternative scenes or of the behind-the-scenes variety. Those are hard to place, so I tend to try to shovel those to the back, but a sub-folder of some kind to dump those would make sorting them a non-issue.