I guess the PSX demo will have the 5 characters announced playable, because the 3rd trailer was called PSX Promo Trailer. And I think it will be 3 vs 3. I'm expecting the two stages shown and probably no more than this.
I'm looking forward some reports talking about the gameplay, mechanics, how the game feels, how similar or different is from XIII, movesets and some images and videos. I would like to see artworks and portraits, introductions, win poses, etc. but I'm not sure if all this will be ready to be shown. The game seems to be in a very first pre-alpha version so I'm not expecting too much of this PSX demo, just a first approach the game basics.