The problem with making a 700c chain tread is making the prototype. Im sure that won't be very easy and extremely time consuming. Now reproducing the singletube 28" chain treads would be extremely beneficial to a lot of us. I have 5 bikes that need them. Hence the fact they sit here. No tires. Or id be riding them.
The 700c tire and wheel combo is a great alternative but very pricey. It all adds up to $600 plus...... vintage hubs replated, new spokes or NOS, hoops either nickel plated or woodgrained, and tires.