There are so many possibilities, but they way I see it is:
If it's anything Keep related it will be fairly brief, as the Keep has been pushed back along with the game, so we know that it still has a bit before it's open to everyone. If there is anything Keep related announced, it will likely be a date, which may or may not qualify as "big news."
Multi-player is some form or another is highly desired by a modest audience and has a good chance of being included for several reasons. One, ME3 multi-player went over well. Two, leaked achievements, though unconfirmed, make mention of a MP related achievement. And three, time. They have had quite a bit of extra time to work on the game, and with that time they would have a better ability to add more features, and with MP being popular, that seems like a likely area to work on.
A companion app would be a great extra for the game and allow for a greater amount of control over your game, not to mention that most people have some kind of device to use with the app. This would be even more highly enjoyed if it allowed control over resources, crafting, etc.
As day one DLC is a no-go, I can't imagine any DLC related announcement, and certainly no new companions, as they said they would not be adding anymore.
Finally, another possibility is that they will give more in-depth description on the other specializations, many people would like to know what Tempest will be like or what being a Necromancer will entail, and that would qualify as "big news" to anyone that is more interested in customization, which is a large number of people.