Designs for this can be found here: 

https://github.com/gnome-design-team/gnome-mockups/blob/master/software/version2/software-installed-app-folders.png
https://raw.github.com/gnome-design-team/gnome-mockups/master/software/version2/software-installed-selection.png

The ui part of this work has been pushed to the wip/folders branch.
Still need to implement writing of menu files.

I've pushed an almost complete implementation to this branch now. It uses a single setting as backing store - this setting needs to be provided by gnome-shell to be effective, the current schema in gnome-software is just for testing purposes. 

Also still missing: reading of directory files to get translated names for standard folders.

I've merged the branch now. Until gnome-shell actually picks up the changes, the functionality is hidden behind a TEST_FOLDERS environment variable.

filed gnome-shell bug 719320

Why can't it be as simple as dragging and dropping one app over another to create/include an app in a group in the GNOME shell app panorama?

This and custom sorting would make the experience so much more user-friendly...

And all enabled now, thanks Matthias.

(In reply to comment #7)
> And all enabled now, thanks Matthias.

I'm sorry, but I have to agree with Rafael Luik, managing this from Software makes no sense what so ever. It's a GNOME-Shell specific behaviour, why should it be controlled from within Software which - if I'm not mistaken - is supposed to be a shell-independent app? Why not just manage this like Android/iOS with the drag and drop behaviour which is much easier to access and have this be a Shell feature instead of Software feature?

(In reply to comment #8)
> Software which - if I'm not mistaken - is supposed to be a shell-independent app?

GNOME Software is designed to be used in the GNOME desktop. If it works in XFCE or MATE that's more of a happy accident, and it's had no testing at all used like that.