I am not holding my breath for a trailer; something like this, I think, would be revealed at a much more high-profile event. Not saying that N7 day is not high-profile (I have ALL of the T-shirts and not a shred of regret. Or shame), but I have my doubts as to it drawing as much attention as, say, an E3 presser.
I would, however, be thrilled if we got to see some more appropriately vague-but-interesting new concept art, some tech designs, like ships or vehicles, or even guns would be nice, maybe a touch of info about how the armor works (since they have been trumpeting the fact that it "layers" for so long now my California-soaked brain views it almost as a challenge; come on, Andromeda, layer-off, you and me! YOU KNOW IT NEEDS TO HAPPEN). And while I really do not think they will reveal any new characters, and definitely not races, getting an in-engine shot of something already confirmed, like the krogan, would not hurt either.
Oh, who am I kidding, my inner easily excitable idiot keeps clapping and giggling in glee and jumping up-and-down demanding a 15-minute showcase of gameplay, complete with dialogue segments disclosing the identities, entire personal histories, pet peeves, preferred pasttimes and embarrassing sexual kinks of all our future squadmates. And ship crew. And the janitor. And their pet amphibious puffer fish.
Totally going to happen, you guise, just you watch.