You CAN do that with Nova launcher!
I've been doing it for a while. It's a little tricky because you can't do it by just dragging a folder into a folder on the home screen. You have to do it within the settings under App Drawer -> Drawer Groups. There you can select a folder to be included in another folder. If the parent folder is on your home screen, than it will now contain the child folder.
I was searching to see if any other launchers can do this, but haven't found any others.