We talk all the time about wishing that manufacturers would do X to the cases. Why would it get anyone's shorts in a bunch to wish that a company might offer a non-leather option? You don't have to buy it, right?
As I said, there are other manufacturers who make book-like cases out of other products such as linen, waxed canvas, etc. If someone wants to expand their market, it doesn't hurt to ask them if they have any plans to make book-like cases made out of animal-friendly products.
I assume you both have asked Twelve South to produce such a product?