Hiroshi Sakamoto, a Sony executive from a non-PlayStation division, has said in an interview that a reveal announcement for the next PlayStation console, codenamed PlayStation Orbis, could take place at E3 or even earlier, in May.
Talking to El Mercurio On Line, Sakamoto said when asked about the PlayStation 4 that, "it's still a big secret, but our Sony PlayStation friends are getting ready. I only can say that we're focused on the games related E3 event, booked for June. The announcement can take place there or even before, in May."
This interview has been translated so it could be that there have been a few translation issues, however it does seem likely that Sony will reveal the PlayStation 4 sooner rather than later.