We know the Legions that will appear in the book are; Salamanders, Night Lords, Word Bearers and Iron Hands.
The Salamanders have the Firedrakes Terminator squad, no images as of yet though. The models may not have even be started currently, but they were play testing them as of the Heresy Weekender.
Models for Kor and Erebus are under construction and it is my belief they will be at Games Day and would even wage money on it.
The Legion has the Ashen circle Destroyer Squad (under construction); this poses a dilemma for me though. As all Legion lists in Betrayal only had one specialist squad it leads me to believe the Gal Vorbak might not be in this book but the Calth book or later (could be wrong though).
Lorgar might have Bitch-Lorgar rules and Chaos imbued-Lorgar rules (this was being trialled and heard it from the Alan Bligh at the Weekender).
Gorgon Terminators; we saw you like Terminators, so we put Terminators on your Terminators and got you the Terminator Terminator. These will be insane. I wonder if they will be 2+, 3++.
Ferrus will be at Gamesday. This is certain for me too as the board is being worked on still and they would want to integrate the Diorama that Simon Egan is working on into the board for display. The Gorgon will be there, so should be the Morlocks (1st Company). If this is the case then that means there may be no specialist rules for the first Company units; I can't imagine any Legion having 2 Specialist Terminator units. So maybe it will be a Battle formation of some sort or maybe a doctrine to field a Company of them. Forge World could just be releasing a set of Cataphractii Shoulderpads and bionics to upgrade the Cataphractii Terminators to Morlocks.
I can't imagine Curze being released for another 6 months (might see him and Lorgar and the Heresy weekender or the open day).
There will be some terrifying early Raptors and hopefully the Atramentar.
As I am collecting the Night Lords as my second Legion I cannot wait. Especially for everyone's favourite starfighter riding psychopath Sevatar. I do hope it is also Sheng they release too.
Supporting other Legions - Updated
Now here is an interesting turn of events. We have the Phoenix Guard and Karkophoni being worked on, so we should expect to see them at Gamesday and in this forthcoming book too. So that is a total of 3 specialist squads for the 3rd Legion, so we should expect more support in future books of Older Legions.
If the Karkophoni is being created this leads me to expect that either Julius Kaesoron and/or Marius Vairosean will be created and that their rules will be in this book. Still no sign of Tarvitz or Lucius models (Lucius could have rules in this book though instead of one of the Captains above, which would make a lot of sense).
We are still awaiting Fabius and his creations too though :) but these should appear later in what I can assume as a series of books which detail the fights going towards Terra (WHICH WOULD BE EPIC FORGE WORLD!!). This would bring the specialist squads for this Legion to 4 between the Heresy inception and the Siege of Terra. Now if this is the case then we should expect similar for other Legions.
Sons of Horus
The Reaver attack squad has been released. So this is 2 Legion specific squads for the Sons of Horus now, could there be another coming to make this up to 3? Or will it come in a later book?
So if an Emperor's Children character is created then I would have to assume rules for another one or two Sons of Horus Character may be found in this book (as they have been released in packs of two thus far). But who? I would stake money on Little Horus and/or Falkas Kibre (who Forge World would have a lot of freedom to flesh out).
Expect to see experimental rules for the Castellax coming soon. This is because they are ready for release and they have just released the Whirlwind Experimental rules. 2 months to test and update into a book and print is not a lot of time.
23/08/13 - They have been released now but no rules. Book is round the corner :)
I expect to see Typhon and maybe the Grave Wardens in book 2 (Maybe a doctrine required to field their Company - similar to the Morlocks above). I would also expect to see an Apocalyptic Destroyer squad in Book 2 too, possibly a unit such as "The Graven" as have just read "Distant echoes of old night" Mk3 Destroyer Legionaires would look amazing too.
23/08/13 - Think book 2 now
I would expect to see the Devourers (Angron's Bodyguard) and another murderous looking unit too. Maybe it's time for a Khärn sandwich too.
23/08/13 - Think book 2 now
Can't wait 'til Games Day now. We will be posting pics on the fly regarding the Massacre book and the Forge World section at the event. Looking forward to having my chatting time with the designers and will be quizzing Alan a lot on this new book hopefully too.
Exciting times ahead for our favourite timeline.