I hate this terminology. If the US has, in fact, "finished" developing, then the future of the S&P will be bleak. I don't think that's the case at all, though. I think development has just started and we'll see fantastic advances in bio-informatics, solar power, 3D printing and a number of other fields in the upcoming decades.
When I was a teenager, I pirated music. I seriously hope my children pirate gourmet cheeses and burritos as teenagers. I download apps that organize my notes. May they download the bio-app that lets them dunk from the free throw line.