Why not....

Sony:

1. The Order 1886 demo is shown and release date is announced (Q4/2014), displays awesome destructibility and physics, immediately restores the faith in the game some people have lost. :D

2. Uncharted 4 demo/trailer. New graphics king? New graphics king!

3. New Guerilla game is shown and looks very interesting. Departure of Killzone is very welcome.

4. New SSM game is shown, probably GOW. Kinda disappointing, because it's not a new IP.

5. New demo and release date for Deep Down (Q4/2014)

(6.) Final Fantasy XV demo is shown and it still looks awesome, release date announced for Q1/2015 (this is more wishful thinking)

Too early to say. There still haven't been any of the usual (and unvelievable) rumors that precede the show, but

Nintendo

1. New third party exclusive game from a japanese developer for WiiU
2. New WiiU sku with more memory (64Gb more likely) in both black and white. Same price.
3. Reveal of the DLC plans for Mario Kart 8
4. Announcement of the aprox. launch date of Monster Hunter 4 in the West
5. Reveal of a new Free to Play game.

Sony

1. New footage of DriveClub along with new info on how it will use Morpheus and an estimated launch date
2. New Guerrilla IP
3. New game from Naughty Dog
4. At least one new third party exclusive
5. Agent will be shown (j/k)

Microsoft

1. Halo 2 HD remake (I'm not very original here)
2. New Fable game
3. New or extended partnership with a media content provider
4. New Kinect game/app
5. New XboxOne sku with a 1TB HDD at the same, current price that will coexist with the current 500GB model that will have a $50/100 price cut.

Third parties

1. CoD 2014 revealed, with timed exclusive content for one console (more likely the XboxOne)
2. New FPS from EA that substitutes Medal of Honor in their plan to have 2 games competing with CoD (there won't be a new Battlefield this year because...)
3. Mirror's Edge 2 will be revealed
4. New game from Take 2.
5. Ubosoft will reveal a new Just Dance... and yes, there will be dancers on stage.

Sony will show / talk about
The Order 1886, Viacom digital cable deal, PS Now, new exclusives, uncharted next gameplay/cinematics

Microsoft will show / talk about
TV, TItanFall, 3rd party exclusive deals, Halo next game play, kinect games

Nintendo will be mostly quiet
please be excited

edit - Sony will also announce that it is either giving away knack or killzone with PS+ on PS4

Nintendo: Zelda U, a new mass-market focused IP, X's name, a mild hardware redesign (either Wii U or 3DS).
MS: XBOne price cut, a new IP from Epic with timed exclusvieness, another paid exclusive 3rd party title. Halo 5 shown.
Sony: Uncharted 4, a family focused title and some stunning third party exclusive content - I'm guessing COD2014.

Oh yeah, and EA reveals some type of Star Wars content.

I forgot all about that Star Wars battlefront... I think it will be releasing next year, and possible titanfall this year for ps4 in fall

From Nintendo

1. Zelda U
2. Pokemon NFC - Pokken Fighter
3. Star Fox Developed by platinum games
4. Animal Crossing U
5. Miyamto's New IP

Other companies - not bothered to make a list- hopefully microsoft or sony can finally reveal something that would convince me to buy their new systems

Games!

Microsoft

1. Halo 2 Anniversary (with access to Halo 5 beta)
2. Forza Horizon 2
3. Resident Evil 7 will be exclusive to Xbox One with MS funding development
4. Platinum Games exclusive new IP
5. Gears 4 teaser
6. Crackdown 3 teaser
7. Banjo-Threeie teaser

If NEITHER Metroid Prime 4 (altho I doubt it since retro just finished DK), Star Fox or F-Zero is announced, I'll be so pissed at Nintendo and I'll stop supporting them the way I'm currently doing. So I think atleast one of them will be announced, they pretty much have to at this point.

Also Zelda U and maybe Pokémon X/Y 2 or Z.

1) Zelda U

2) F-Zero

3) Pokémon X/Y 2 or Z

4) Kirby on Wii U

5) Star Fox