honestly by that point there wasn't that much left of interest to me in regards to the Forsaken. Not sure what would have qualified as a "bombshell" either.
Here's who was still around by that point:
Demandred/Boa: Killed by Lan
Graendal/Hessalam Bounceback compelled fighting Aviendha (can't remember if she died or was just essentially a mindless slave at the end)
Lanfear/Cyndane: Killed by Perrin
Moghedien: now a good damane
Moridin/Ishamael: Body swapped with Rand
Taim/M'Hael: Killed by Egwene
Dead before AMOL:
Aginor/Osan'gar: Killed by Elza
Asmodean: Killed by Graendal
Balthamel/Aran'gar: Balefired by Rand
Be'lal: Balefired by Moiraine
Mesaana: Mind destroyed by Egwene
Rhavin: Balefired by Rand
Sammael: Killed by Mashadar
Semirhage: Balefired by Rand
Given that it sounds like there was very little fan-theory around this I'm inclined to think it doesn't involve Demandred since he was the subject of a million theories and a novella. But then, Sanderson also seemed to be more deeply involved with this character than the others so perhaps he's more in tune with that?
Lanfear, aside from the Cyndane discussions and her drop in power, seems relatively unexplored theory territory, so perhaps we missed something there?
I wondered what happened to Mesaana as it's never mentioned again. It wasn't really covered in the last book. I suspect she was nursed like a profoundly incapacitated person for the rest of her natural life?
It's also not mentioned whether Graendal died, but I suspect she was healed. Graendal would actually be a good source of information - she'll spill the beans on anything, especially if Aviendha asks her anything.
I can't think of anything useful that BS could tell us, and even so, I'm not prepared to spend any more money on this series. The Companion is a disgrace. I feel like a darkfriend just for reading it. I think RJ would be very unhappy if he was resurrected and saw what had happened since his death.
I suspect the Aes Sedai keep Mesaana alive as a symbol of their might, you know how much they loved to trot out defeated enemies 
Seems like an odd omission to have Graendal's fate technically unresolved given how big of a role she played in the LB, I'll have to go back and reread that scene at some point, but I agree that if she is alive she's too good of a resource to leave unused!
I think there is some twisted sense of balance in Graendal being captive to Aiel, Moghedien to the Seanchan and Mesaana the Aes Sedai. I still find RJs reluctance to kill off the women odd ... Moghedien's fate is by far the worst of all of the Forsaken IMO, Graendal and Mesaana aren't cognitively aware enough for them to really suffer for their sins and the others all had relatively quick deaths. I wish we had a few Forsaken still on the loose actually ... would have made the story feel like it was still open ended. As it is I feel like the whole thing got tied up in a "nice little bow".
I feel you on how the companion turned out ... felt very much like a bait and switch sales job. Not at all what I was expecting to get and it makes me mad. I may sift through it again to read all the entries for the individual nations, maybe if I'm bored I'll build another spreadsheet with pertinent factoids
