wow… this seemingly fundamental request is now nearly 4 years old. I came here after just inserting 48 images into the resources panel and finding, not just that I can’t organise them into a subfolder, but that each of those images creates it’s own folder even though there’s only one file connected with it (no retina images needed for this project). Not only that, but they are all open by default which means your resources panel suddenly becomes a very long list indeed.
That seems kind of mad to me.
What I did discover is that if you highlight all those subfolders and hit the left arrow key on the keyboard, you can collapse them all at once which is somewhat of a comfort.
Oh… and while I’m at it, the ability to drag a folder into the resources panel which would appear as a folder would be very handy. Particularly if you’re going Hype insists on every image being forced to be in its own folder.