I'll be following to see how this works out. I was thinking of designing and machining my own vise, based on the accessory vise that you can get for the Nomad. The problem I found is that buying a proper dovetail cutter makes it cost prohibitive for a one project use. Most dovetail cutters are only available in 3/8" or 1/2" shanks. I couldn't find one for a 1/4" shank that didn't have a tiny cutting diameter on it. Probably a good reason for that.
If you change your design to an acme screw with just threads in one direction, it seems like this might be pretty reasonable cost wise. I looked into buying a machinist vise and everything is either professional shop grade (and hundreds of dollars minimum) or it is a cheap drill press vise made of chinesium. Very hard to find a well made, affordable machinist type vise for the hobbyist. Probably not enough market yet to justify a company making them commercially.