I don't see a market for that one. Perhaps 20 a year?
I have another product idea even if it is completely off topic:
What about a basic "small" 8x10 enlarger which fits on a desk with normal room height and allows a 20x24 enlargement with a 240mm lens? All those used Laborators etc. are huge monsters which do not fit in most darkrooms. I think that could have a potential market.