The assumption you used helps to answer your question. "at a profitable rate" So this assumes that the chicken-and-egg electric car/infrastructure can evolve

The assumption you used helps to answer your question. "at a profitable rate" So this assumes that the chicken-and-egg electric car/infrastructure can evolve together profitably while reaching critical mass. (To be sure, I believe they can, but it will take either government or brave investors to get there.) So the question really is "can $6T be divided up into the cost of whoever is paying for it, i.e. electricity users to maintain profitability as it is built?" If you assume the answer is yes, there is no question! (As for the "maintaining the grid", yes, obviously we are already maintaining it profitably. No need to build critical mass/adoption or initial infrastructure investment, so no interesting stories to write!)