This question has been asked many times on this site. How would you offer this in a way where publishers aren't screwed over? Onlive is really the only method for this to do it properly as you don't get the actual game data files on your PC.
PC Rentals = 2 things
Mass Piracy, no more desire for a publisher to put out games on PC.
Mass Piracy: Once you get the game data files on PC easy to patch and keep game for free.
No incentive to put on PC: Why would anyone buy a PC game anymore if they can "rent i.e. Pirate" said game for a much smaller fee. I wouldn't put a PC game out if I knew that everyone was going to rent it day one, where would the money I make be?
Here is the truth. Going digital means rental models going away not new ways for rentals. Game publishers are looking to go digital so they can make more money per game, not make it so you never have to pay for a game again.