This would be such a time-saver. Not every user renames images before uploading to Marketo, and it's such a pain to have to go through all of the "Screenshot 2015-01-01 at 12:00AM" files and figure out which is which. Being able to rename files would mean that you'd only have to do that once, and then it would be searchable from that point onwards.
Bumping this. Really need to be able to standardize on names, especially when you have agencies doing work and designers naming images "Email 2" or some such bad name.
This would save so much time that is currently wasted downloading/deleting/re-uploading. In order to make it happen, you could uncouple the URL from the item's name (two separate attributes). It would be a big improvement!