Its going to be hard to reproduce an old design to a quality level that would satisfy customers, plus there is the issue of the aditional origenal parts needed: wheels, tires, fenders, motors ect.
What would be cool would be an updated version of an old design using modern wheels motors shocks and brakes. I personally love the 10 to 12 inch rim 1970s full suspention bikes like Rupps Speedways Foxs Bonanzas ect. They ride great, seeing a new take on this idea but updated would be realy cool.