Microsoft:
Halo 5
Rise of the Tomb Raider
Phantom Dust
Halo Wars 2
Gears of War
Scalebound
Crackdown 3
Banjo-kazooie
Select indie games
Forza 6
3rd party games
New Xbox dashboard

Edit: I think Halo Wars 2 and Banjo-Kazooie would be the two big announcements for the conference, oh and Gears of War. Could get a few new IP's announced. 

Sony

Gran Turismo 7
Guerrilla Games New IP
Sony Bend New IP
Project Morphues

Microsoft

Gears of War
New IP
New IP
Game Streaming Service

Nintendo

Sequel to Mario 64
Sequel to Donkey Kong 64
Pokemon MMO
Game Streaming Service

Launch trailer for XENOOOOBLAAADEEEE.

Most definately a third party, and most likely platinum games. Literally no reason why nintendo wouldnt want them to help make it as it's what kamiya and the fans want, and they need to make amends with the fans.

Sony:
- Uncharted 4 gameplay
- No Man's Sky final push and release date
- Sony Bend's new IP
- Guerrilla Games' new IP
- Level 5's new IP
- Huge indie showcase

Microsoft
- Forza Motorsport 6 announced
- Halo 5 gameplay blowout
- Quantum Break and Tomb Raider footage and release dates
- Rare announces a major new game
- Twisted Pixel's new IP
- Gears of War debut trailer

Nintendo
- Animal Crossing for Wii-U
- Next Level Games' new game
- Star Fox blowout
- Zelda blowout
- Something from the Mario team at EAD Tokyo
- Begin teasing their next hardware