Not for a long time. There is no reason to release one, since the current PS3 is just starting to tap into it's capabilities.
As far as new features, the PS3 has the ability to be upgraded with accessories and software. So, releasing a PS4 would be redundant, and leave a lot of current ability to waste. They're better off waiting for the 360 to hit it's technological cap, forcing Microsoft to release a new system, while the PS3 just keeps getting better.