I think you're vastly underestimating the economies of mass production and the complexity costs of even templated or made-to-measure items.

Yes, you'll see some degree of custom manufacture, as exists now in furniture and a few other areas. But in too many cases, the costs of mass production and available efficiencies are simply too great to compete with.

Apple's devices, as an example, are not custom-specified, but are offered from an exceptionally small number of variants.