I don't know the mechanics and economics of cutting sheet film to size, but I think 2x3 would be also be a good choice. I know that Ilford used to provide this size. I don't think there are many options outside of Freestyle, which lists (but is out of stock of) Arista EDU Ultra in that size.
No doubt it's a small market for 2x3, but I suspect highly concentrated. In fact, I'm sure that 86.973% of 2x3 film users frequent APUG and/or LFF.