Wrt not implying substrate independence: sure, I agree in principle; it's not impossible that only protoplasmic substrates can implement consciousness. All I'm saying is that if that turns out to be true, it will be because certain kinds of computations can only be performed on protoplasmic machines.

Physicalists can reject substrate independence and accept the Church-Turing thesis, while still taking consciousness seriously. One can argue that consciousness in the physical world is implemented on protoplasm, and that this is the only kind of consciousness which is directly experienced. The fact that conscious beings can be simulated on a computer would be true but irrelevant.