It would be really nice to know how much of these different formats sell - the J&C list doesnt list half plate (which I would buy) but does list whole plate (and it doesnt seem to be a strictly ULF list as it has 6.5x9cm).

Gandolfi will make them, but you see very few around compared to half plate - I saw a whole plate studio portrait camera for sale in Portobello market a few weeks back, first I have ever seen (no plate holders, listed price a bit expensive), but there are half and quarter plate cameras constantly on ebay in the uk in varying conditions, and in shops.