I don't think these people get the point. You're not asking if they'll stream movies, that's obviously not their thing. You're asking if you can digitally download and rent the game.
Problem with that is you'd be essentially getting all the games for free. You'd download them on your console and bypassing any security they have would be trivial.
There would also be problems with download servers being overloaded, long download times, the rental service itself, etc.
Gamefly obviously doesn't have enough revenue to get it's shipping up to speed, so aside from the other problems, adding a game streaming service is out of the question, at least until technology improves again.