Sony just announced the Playstation Now, enabling streaming of PSOne, PS2, PS3, and PS4 games to your PS3, PS4, Vita, mobile phone or tablet -whether if you have a Playstation or not - so expect a monthly fee for this service.
A closed beta will start in the end of January, and they believe that it will become available for masses (In the USA only in the start?) In summer 2014, according to Andrew House, President and Group CEO of Sony Computer Entertainment.
UPDATE
Playstation have wrote more details on their blog, read it here http://blog.us.playstation.com/2014/01/07/playstation-now-streaming-game-service-coming-this-summer/
The most interesting thing is, that this feature is on the PS3 and Vita as well, meaning that you probably can end up playing Killzone Shadow Fall on your PS3 and The Last of US on the PS4.
