It would be very cool, as well as more compatible with WordPress architecture and most themes, to make plugin able to pull images from a post gallery. This makes more sense, to me at least, then needing to turn on custom directory option, create new folder via FTP for every new post, manually upload images, and add different custom field to every post in WP admin. If you like to use thumbnails for your posts, you are also required to create each of them manually. WordPress has functionality built in for uploading, thumbnail creation and re-sizing, setting image order, etc., why not use it? Also, should you ever change your mind about which plugins or themes you use, you will be able to transition easier.