Ben and Vestara seems likely and I don't know why. And I like the Jaina Jag marriage thing. I think they could get married in Allies actually. It could adhere to that.

...A Sith Fleet warring with the GA in some super intelligent way enhanced by extremely powerful Dark Side abilities that makes them more than a match for what the GA can throw at them. I foresee Mandos appearing, but on whose side I do not know. And I also see the Jedi holding out to bring Daala to the bargaining table. Then again, the Jedi might be so split with internal strife due to the insane Jedi disease that they can't help anyways. Climax of the book will be Ben vs Vestara.

Of course I could be very wrong.

I honestly think Ben will succumb to the psychosis. I think that's what the title BACKLASH means, and I agree with you that ALLIES may pertain to Daala reaccepting the Jedi Order.