Until you have some (primitive) models stored somewhere in such a fashion that you can find them and reuse their components, you are, by definition, making-to-order,
a “waterfall.” It is only a matter of how wide or narrow the waterfall is and how
many times you iterate through it enroute to implementation. That is, you are never
going to appreciably reduce time-to-market until you have something in inventory
before you get the order. In manufacturing, this would be called “masscustomization”,
assemble-to- order.