They won't be anything new for KH3 IMO, they said they announced it too early.

FFXV should have gameplay footage and details tough.

There will be quite a mix of new and old stuff i'd imagine.

Uncharted will be shown
Hopefully The Last Guardian
Santa Monica may show something if they had another game far in development other than the canceled game
Guerilla Games also has a new Ip in developement that will either be shown this year or next year
Media Molecule has also been working on something
Sony Bend as well

So there is 6 possible games from first parties right there. Then i expect them to show some third party stuff as well.  It all depends on how far all these games are indevelopement.  I think it is pretty safe on betting on Santa Monica, Uncharted, and Media Molecule all being shown. 

I think Guerilla said in a video that their new IP has been in development for 2 or 3 years now, so I think there's a pretty good chance of that being shown as well.

a little over 2 and half years now. there is a good chance we will see it this E3, hopefully. Sony Bends game has been in development for the same amount of time or even more now. hopefully its NOT a syphon filter game. 

What I'm hoping:

• Naughty Dog with Uncharted 4 for the PS4: Q2 2015.
• New Guerrilla Games IP for the PS4: Q3 2015.
• Team Ico with The Last Guardian for the PS3 and PS4: 2015.
• Media Molecule game, possibly Little Big Planet 3 for the PS4: Q1 2015.
• Sony Santa Monica game, possibly a new God of War for the PS4: Q3 2015.
• SCE Bend Studio game for the PS4.
• Playstation Now stuff.

What probably won't happen:

• Game from SCE Japan Studio (Knack developer).
• GT7 tease from Polyphony Digital.
• SCE London Studio's game (Playroom developer). The game is described as an 'AAA character action game'.

A whole list of other things I'm hoping for, but some highly unlikely:

• Sony buys Ready at Dawn, Housemarque and Quantic Dream. Quantic Dream's last non-Playstation exclusive dates back to 2005, Ready at Dawn's back to 2008 and Housemarque's last console game that wasn't on a PS platform dates back to 2008. Both Quantic Dream and Ready at Dawn's announced games are PS4 exclusive. At this point, they might as well become 1st party.
• inFAMOUS: Second Son DLC announcement.
• Resogun DLC announcement.
• DriveClub releases on June 12th.
• The Last of Us GOTY edition announcement/release for PS4
• Possibly more ports, like the Uncharted and inFAMOUS franchises.
• Call of Duty DLC first on Playstation platforms or some other deal. This was rumored to be happening due to Activision supposedy attented the Playstation Destination event, the Playstation 4 outselling Xbox One and Destiny deals between Activision and Sony.

A man can dream, can't he?

Media Molecule are working on a new IP. 

i doubt Sony Santa Monica will show anything, the PS4 game they teased was cancelled (stigs game). and Cory barlogs game is still way to early in development. unless they had a third team i doubt they will be showing anything. specially that SSM released GoW:A last year.

Doubt we will see a GT7 reveal, specially with DriveClub on the horizon and GT6 releasing just last year. Next E3 its a big possibility though since Polyphony digital said GT7 will be either a 2014 or 2015 tittle, way things are going 2015 seems more likely.

this is the first time i hear about sony londons action game, got any sources?

i doubt sony will announce they bought two studios at E3. but we might get a glimpse at what Quantic Dreams PS4 game is. it started development in mid 2012, so its been in development for 2 years now. 

Agent, The Last Guardian, and BioShock Vita.

what about 8 days?