I’d like this feature also. It could be used for future features. Like adding tags to multiple photos in the same time.
For the time being you use the desktop client and move the files around in the synced folders. It works rather well in my opinion.
Select one file, then go to Actions → Select file range . I have NC 21. I don’t know if it’s possible in other versions.
In the Files you can do this, not in the gallery