All it will take stream massively-watched video at orders of magnitude less cost than either airwave or cable broadcast is TCP multicast. Granted there are some barriers there, but it's fundamentally more efficient than any other broadcast method. It just hasn't been worth it yet because for those few events we've already had long-existing broadcast TV networks.

Hell, you could even do it purely at the application level with BitTorrent.

Cable is cheaper now because of sunk costs, but cable companies are much too fat to innovate at this point. They will do whatever they can to keep prices high and cling to their cash cow, while Internet bandwidth inevitably becomes cheaper fueled by thousands of disparate interests. Cartels may drag out the endgame, but eventually content producers will have no choice but to go where the eyeballs are.