Well, this could dramatically increase the demand for tantalum, which (econ 101) could dramatically increase the supply over time? Is tantalum in much demand today?
Tantalum is in demand today, yes. Tantalum capacitors are a well known application, but it is used in all sorts of things.
My point was that even if tantalum were free, a material that is 96.5% copper is still not going to be significantly cheaper than copper, which I think is a pretty self-evident outcome.