Considering it's IGN, I doubt they'll reveal a character like Fujin, Reiko, Tanya or someone like that from the post-MK 3 era simply 'cause those characters aren't very well known to the casual MK audience. I'm going to guess it'll be someone like Mileena, Reptile, or Shang Tsung. Someone that's still fairly known, even to casual MK fans. Although, this could be a good way of getting this seemingly new character with the bow over with both casual and hardcore fans alike.
This stream on Friday (Saturday for me) though I have high hopes for. Seeing as how almost certainly everyone tuning into that stream will be a more hardcore fan of the series, them revealing a character like Fujin, Havik, Bo' Rai Cho or Reiko would make sense 'cause we would all know who they are.