During a lecture at a university EA's Frank Gibeau has confirmed that EA and DICE (presumably) are working on Battlefield 4. It's the first time the game has been mentioned officially, even if it was only a matter of time.
The fact that EA are already mentioning Battlefield 4 is an indication that we won't have to wait as long as we did between Battlefield 2 and Battlefield 3. And perhaps it's also an indication, that EA and DICE are moving away from the Bad Company series for the time being.