How is anthropic reasoning affected by the existence of a conscious stone that nobody and nothing can ever communicate with, even in principle? If it is indeed affected, then this says bad things about anthropic reasoning.

But I don't think it is: Some smart LW poster once noted (I can't find the link now) that for anthropics all is needed is an agent that can do a Bayesian update conditioned on its own existence. An agent that can do this does not necessarily have consciousness under any reasonable definition of consciousness.