I'll give this a go:
Sony
- Uncharted 4.
- Destiny Expansion.
- Street Fighter V, new characters announced.
- Final Fantasy XV.
- Star Wars Battlefront, timed exclusive DLC.
- Tony Hawk announced.
- Indie segment (4-5 new announcements).
- Full Throttle Remastered announced.
- Metal Gear Solid V.
- Metal Gear Rising 2 announced.
- Ratchet & Clank.
- Level 5 JRPG announced.
- Guerrilla Games' RPG announced.
- The Last Guardian re-revealed. I've been predicting a 2015 unveil for over a year now. It's nearly two years after Japan Studio's last two games (Puppeteer and Knack), so the timing just seems pretty good.
Microsoft
- Indie segment (a couple of new announcements).
- Call of Duty, timed exclusive DLC.
- Halo 5.
- Forza 6.
- Quantum Break.
- Fable Legends.
- Scalebound gameplay footage.
- Tomb Raider.
- Rare's New Game announced.
- Battletoads announced. Not developed by Rare.
- Gears Trilogy announced.
- Gears 4 announced.
- AC Victory.
- The Division, exclusive DLC.
- Deus Ex 4 announced, timed exclusive DLC.
- No Crackdown or Phantom Dust.
Nintendo
- Indie segment (a couple of new announcements).
- Zelda.
- Star Fox.
- Devil's Third.
- Mario Maker.
- Xenoblade Chronicles X.
- New Mario Game.
- Super Smash Bros DLC.
EA
- Still sticking with their dumb "behind the scenes" idea, despite no-one except EA execs apparently liking it.
- Mass Effect.
- Mirror's Edge 2.
- Star Wars Battlefront.
- Need for Speed.
- Criterion's game gets a name.
- UFC 2, Madden, FIFA, NBA Live and NHL shown.
- Sims stuff.
- Bioware's new IP, Battlefield 5 and Visceral's Star Wars game teased but not announced.
Ubisoft
- A couple of small UbiArt games.
- AC Victory.
- The Division.
- Just Dance.
- Rainbow Six Siege campaign gameplay.
- Watch Dogs 2.
Bethesda
- Fallout 4.
- Dishonored 2.
- Doom 4.
The third party deals could go either way, I just based the new ones on the last deals they had (so Battlefield Frontline -> Star Wars Battlefront at Sony's conference, Tomb Raider -> Deus Ex at Microsoft's).
Two Sony first party announcements (Level 5 and Guerrilla's RPGs) plus two unveils (TLG and R&C) seems about right to me. Anyone thinking Sony are just going to announce everything are living in a fantasy land, they very obviously like to spread their announcements out between E3, Gamescom, TGS and PSX. Sony are still pretty tight with Konami and Kojima, so if Rising 2 is announced anywhere this year, I'm guessing it'll be here.
For Microsoft, the Gears announcements are predictable. Battletoads has been hinted at, so I wouldn't be surprised to see it and I figure they'd probably outsource it like they did to Killer Instinct. Platinum are a really fast studio, so even though the game has probably only been in development for just over a year, I'm guessing we'll see some gameplay of that. But I don't think we'll see any Crackdown or Phantom Dust. The latter for obvious reasons and the former because I doubt it's ready to show.
Nintendo will just be Nintendo, I'm not sure what to expect other than Mario games and probably some Smash DLC.
EA did the same "behind the scenes" bullshit at Gamescom that they did at E3 last year, so I'm sure we'll see more of it. They should have a bunch of new games to announce/reveal, plus I'm sure they'll tease some new ones that we all know are coming.
Ubisoft will be Ubisoft. Same shit, different year.
Bethesda has to have at least a couple of games, including a major one, to justify the expense of a conference. So I'm betting on Fallout 4 being one of them and of the other games we know are in development, Dishonored 2 and Prey 2, I'm leaning towards Dishonored 2 as another game they'll announce.