[taneq]

Why do you need a superfluid? It sounds like all you need is disc in a vacuum that you suspend/rotate like the armature of a motor.

Until, of course, it gets nowhere near the speed of light because the limiting factor to spinning something fast isn't friction, it's the required centripetal force to keep it in one piece.

And assuming you could solve that by making the spinning thing out of unobtanium, you're still not doing anything to break conservation of momentum.

[fastball]

But is that not why he is using a fluid? A fluid does not have intermolecular bonds that need to overcome the centripetal force, so it shouldn't be a problem?

[taneq]

It still has inertia, and as you point out it has the added disadvantage of having no internal structure to help hold it in place.

Put a plate in the center of a turntable and pour some water into it. Now rotate the turntable, slowly accelerating. What happens to the water?