I might be one of the few people here that doesn't think we'll see anything Killzone 4 related at the meeting.
Then again I'm not a fan of Killzone but I still don't think we'll see KZ4 at the event.
Guerilla Games has to be there, their last game (Killzone 3) came out about 2 years ago now.
Since then, they must have at least one team working on a new, next gen Killzone.
If GG are for whatever odd reason not at this event, they will surely have a large presence for Sony at E3.