thought experiment to demonstrate materialism is incomplete

I think the usual zombie argument assumes a bit much. What about this much milder thought experiment: you stand next to a puddle of atoms, one for every atom in your body. In scenario A you move to a location X and the puddle doesn't do anything. In scenario B, the puddle form an exact copy of you, then you disintegrate into the exact same puddle at the exact same location, and the puddle body moves to location X. Since the end results of A and B are exactly the same, any truth in A must also be true in B. Yet in A you just moved, whereas in B you have died. An external observer won't know this, the puddle buddy will insist it's you and just walked to X and didn't begin existence as a lump of atoms, but your perspective is very different.

This evades the troublesome question of whether zombies are conscious, I don't see any controversial assumptions made here. Doesn't say anything about consciousness without a brain, but clearly demonstrates a complete description of the material universe is still incomplete.