The room in Space Odyssey
is supposed to be a glaring contrast between the cold, lifeless illumination coming from the floor and the stark and ornate (Victorian?) interior decor of the room itself. Of course this isn't used in the Garage/Batcave, but considering the fact that Nolan flips the floor for the ceiling, and that conceptually
the Batcave is located beneath
Wayne Manor (though of course not in this incarnation but still) we have a visual consistency. The layer above the "layer of illumination" is still conceptually ornate (and Victorian), Wayne Manor
Making this world beneath
the illuminated chamber the Batcave, "naturally" having this "floor of illumination" occupying not the floor but the ceiling.
So what happened to the most important object in the room itself from Space Odyssey
? The black monolith that apparently transforms or "changes" Bruce Wayne into Batman?
Nolan doesn't forget that, he can't (or atleast I can't). The Monolith is still in Bat-Lore just as potent a symbol / device / entity of transformation and change, Bruce uses it/encounters it every time:
It's the Bat-suit, the container that emerges from an even deeper and subterranean (or outer) place from this layered world. It's abysmal, dark, mystical and transformative, promising Bruce's birth into something truly supernatural and monstrous.
The monolith transforms Dave into the Star-Child, the most enigmatic symbol of Kubrick's film. The container transforms Bruce into the Dark Knight, the most profound symbol of terror and hope in Nolan's trilogy.
Stretching it too far? It still makes sense. Nolan's inside-joke is ours.