Also, remember that piece is removable, so you could have a more natural looking stone base for the WR or the BR if you wish.
It's mostly about giving people a few options, a few play scenarios if you will.
I would absolutely be in favor of giving that hole a plug of sorts to disguise it or hide it. Or have another accessory plug into it like... Maybe a Filmation Sorceress throne? Or another weapons stand, or the torture rack?
Ideally it could be a universal plug for other items if Mattel wishes.
If there's another "Grayskull furniture pack" made with the "well of souls" (dungeon grate), they could include said plug or other accessories to make use of that hole.