Well, since most of the bios are up now, we can speculate on the story a little better now.
I think that the source Bo Rai Cho gets help from is Sub-Zero, since they both seem to be up against the Tarkatans.
And I think that Ashrah will go up against Ermac, but this isn't a good vs. evil fight, which makes it real cool.
Overall, I can honestly say that I am really loving this story the best, because this isn't the usual good vs. evil storyline we always get. Rather, every character just seems to be on their own agenda, everybody's human, if you get me. This is turning out to be the most interesting storyline of all the MKs.