I was responding to your claim that « He’s not really measuring FI, just similarity, and since extant species-specific sequences evolved incrementally from ancestor-specific sequences, he can’t justify any conclusion that the extant sequence couldn’t evolve. »
And indeed, Gpuccio doesn’t claim that extant sequence couldn’t evolve nor that they couldn’t have evolved from some ancestral forms. Rather, his claim is that a transition involving the addition of 500 bits of FI always warrants a design inference. This is because the probabilistic resources of the whole universe are insufficient to find a target exhibiting 500 bits of FI from an unrelated state.