Nice point. :)

That said, your example suggests a different difficulty: People who happen to be special numbers n get higher weight for apparently no reason. Maybe one way to address this fact is to note that what number n someone has is relative to (1) how the list is enumerated and (2) what universal Turing machine is being used for KC in the first place, and maybe averaging over these arbitrary details would blur the specialness of, say, the 1-billionth observer according to any particular coding scheme. Still, I doubt the KCs of different people would be exactly equal even after such adjustments.