I would hope Sony leaves some suprise companies and announcements in store. This is almost being hyped to E3 levels considering this thread. I could also see this as just being an E3 Redux for the fans with a shit ton of PS4's and updated builds of current games.
Well as far as games go, we still have the VGX.
I don't only expect games.
A short outlook on some coming software updates would be also nice, and what wouldn't scream more twenty years of playstation, than finally being able to play your psx/ps2 games on your ps4.
Except the rumored emulator for those maybe, but that's also something I might expect from such an event.