I am not a chicken breeder or seller, and I really don't know what I am talking about. However, I do have an idea for the OP.
Seems to me that the best potential market is for small, backyard flocks. It would be a plus to market a breed that is truly rare and provides a good number of eggs with an unusual characteristic. Oddly enough, IMO, what is lacking for backyarders is a good dual purpose, calm, white-egg-layer. If somebody really wants to produce a variety of egg colors, there are dual purpose type breeds that do all shades of brown and greens and blues, but not many options for white. Most of the white egg layers are Mediteranean breeds that tend to be more flighty and noisy.
Which brings me to my idea. Somebody needs to develop some Hollands with the key selection factors being temperament, true white egg color,egg production, egg production and then also I would focus on egg production. In other words, don't breed a show chicken -- breed a utility chicken that lays white eggs, is pretty and is friendly.
Also, seems to me that the barred Hollands are nice looking birds, lay white eggs and are reputed to be friendly, so you ought to have the raw material to work with.
I think these could be marketed on the basis of being both a truly rare breed and an alternative to Leghorns for the backyard flock. You would not have near the competition from big hatcheries, because very few hatcheries carry Hollands. That makes them actually rare.
Anyway, if somebody would breed up some Hollands with a reputation for laying as well as barred Plymouth Rock, I think I'd order some myself.
(My apologies to the Leghorn lovers of America for what I am sure are overstatements about that breed.)
Again, this advice is free for a reason,
Neil