On a technical note, green screen's not that hard for a locked camera/editing, but for a free-floating, move-on-demand camera like the golem has, it would be a nightmare to do even once. To really feel "ooh that's bottomless," you'd need the golem to move up to the edge and look down; to do that live and on demand, I'd expect to pay millions of dollars. That said, I *do* think it may be possible to do *something* with green screens by the time V5 rolls around, but it would be more on the lines of "oh I didn't even notice" or the same kind of effects you might get by building with sets & props.
Come to think of it, at that point, you'd basically be creating a VR space with the golem camera as the headset.
Actually, rather than use a green screen in the space, you could plausibly do one of those animated monsters on a video with no background and integrate it into a room with a real-life set, with maybe an extra layer on top so it looks like the monster is in the *middle* of things and not the front, for a room where the camera is pretty settled in one place for the fight. Likewise, if you were say, in a castle, you could put a green screen in a window and play a video of the fields beyond (or do the same thing with LCDs on a loop in a physical dungeon).
I came here to sing and collect tokens, and I'm alllll out of money.