Here is an idea for a nifty feature that would be useful for photographers: a filter that excludes files from the backup if a file with the same name but different file extension exists in the same folder. Sounds complicated, but the idea is: don’t backup .jpg files if a RAW file with the same name exists. In digital photography, RAW files are like negatives. So if your “prints” (the jpg files) are gone, you can reproduce them based on the RAW files.
Now, I’m not sure if this is a big deal to implement. If it is, it’s probably much simpler to do this selection manually: just make sure that a certain folder/branch only contains jpg files that belong to a corresponding RAW file and simply exclude jpgs from the backup from this folder.
But if it’s easy to implement this with a few lines of code, it would be nice to have.