The most recent rumour published about the PlayStation 4 is that it might be launched on 2013. This rumour was actually very vague as no other detail are available yet.
In a recent report by Develop-Online, various sources “within Sony's internal studio structure” confirmed that teams have begun “preliminary work” on the PS 4 gaming console. Yes, finally something concrete is out there regarding the PlayStation 4. Also, the report mentioned that some of these teams may be moving into the full level production phase sooner than expected.
The report which did not disclose any names -- just leaves it to the world to speculate. The work could involve any studio, the upgraded games may include Sony Santa Monica (God of War), Guerilla Games (Killzone), Naughty Dog (Uncharted), PolyPhony Digital (Gran Turismo) and the very popular Sucker Punch (InFamous, Sly Cooper).
The teams Sony hires with always produce commendable things so it can be expected that they might again surprise the world with their latest product. Sony has always maintained the stance that the life of PS3 is 10 years. However, this statement does not deny that PS 4 cannot be launched or the PS 3 cannot continue after the launch of PS4.