I guess one danger could be that the less reputable breeders may jump on the COI bandwagon (presuming of course they have any idea what it is - I certainly didn't until reading the forum posts -) and use a lower percentage number as a selling point, disregarding other health and welfare factors, eyes, kidneys, temperament etc.
Except the hideous recessive genes that double up to give kidney, eye, neurological and immune-mediated diseases, behavioural difficulties, liver shunt, hyperthyroidism, epilepsy and...to be honest I lose the heart to go on. They are all listed as genetic problems in cockers by scientists and vets (rather than breeder- wonder if maybe they have more knowledge?) and are the result of consistently high CoI!
And I just don't understand a point of view that cares more about coat density than all of this.