What ever your futrue plans are on building these holders for sale Bill, I think there would be demand. There are a lot of folks like me who are either starting in wet plate or very interested that have modern view cameras and a fast lens or two. Even though it is pretty easy to convert a 8x10 holder to hold a plate a nice dedicated holder to fit modern cameras would be desired if one decided to shoot wet plate on a regular basis. Couple that with folks like Bostick and Sullivan who are now selling kits with the all the necessary chemistry it is becoming easier than ever to experiment with wet plate for a reasonable investment.
I know there is a group that likes to keep everything close to period as far as gear goes but since I still shoot film I like the option of shooting a plate and maybe a sheet of film of the same subject with the same camera.