you are the market. quite possibly all 100% of it--this might have been the first, or maybe the second time i've seen any request for it, which is still well behind flip-out screens.. i think it you would need to convince at least half the people running carpc's to get one for any manufacturer to seriously consider making any. which would be better then what the flip-out screens sold to.
carpc's are a very niche market, so it's hard for new products to break into the field because there is such a low return on the investment.
but i encourage you to build you're own and show everyone how awesome their setup could be with it!!