I don't know. They do feather sex the standards sometimes. We were watching Dirty Jobs with Mike Row. He went to Murry Mcmurry Hatchery and they were feather sexing standard chicks.
I saw that Mike Rowe episode. They were vent sexing. Season 1, episode 7. They seemed to like squeezing the poop out of the vent so they could see inside the vent. You don't need to squeeze the poop out to feather sex. You may want to watch that episode again.
They do use feather sexing at hatcheries too. Not with pure breeds but with crosses set up so they can, mainly with meat birds. They could set up breeds to feather sex, including bantams. That would require selective breeding to develop one flock that has the fast feathering-gene to produce the father, and a second flock for the slow-feathering gene to produce the mother, then a third flock to produce the hatching eggs that could be feather sexed. That means after they develop the two grandparent flocks they would have to maintain three separate flocks to produce bantam chicks that could be feather sexed. That does not sound like a profitable business model to me, not with all the different bantam breeds they have.