I would very much like to read about a case in the US where the arguments used to discredit the luminol evidence in this case have been successfully presented in a criminal trial in the US. If this is the first time that these claims are being used to discredit luminol evidence, and the claims are only made by people that would never present the same claims as experts in a criminal trial, then I think it's not worth debating. It takes on the appearance of being a good enough argument for a case in Italy, but not good enough for a US trial ... giving me the impression that it is an argument without substance.
I don't know that the Luminol tests were discredited per se, just that secondary tests did not find dna, there may be other tests to determine what exactly the Luminol did react to, it may have been blood, just no dna was recoverable (or identifiable) for whatever reason - too little, degraded by other substances on the floor, etc).