I've already emailed him about 8x10" and 11x14" holders, so you're second in line, but I completely agree that the panoramic holder idea is a non-starter. Much easier to crop the film after the fact than to cut special sizes in advance and still have to carry a large camera.

I use a darkslide cut in half (actually cut in an "L" shape) if I want to get two panos on a sheet. The darkslide was free (a cracked one I got from a friend), and cutting it carefully was about 20 minutes work.