They'll announce the PS4.
Loads of developers including Hideo Kojima will come up on stage and say they approve of this console and might make a game for it in a couple of years.
Drop the price of the Vita.
Then just as everyone is expecting that this time surely they will have showreel of new upcoming games...they will cut to a reel games already released (CoD Declassified, AC Liberation, Gravity Rush) and just say "there has never been a better time to own a Vita!" Proceed to drop the mic on the ground and walk out.
There you go, that's pretty much what will happen. Just imagine it dragged out for 2 hours.