Well, look what Warhammer Community brought us today! They have a post on the detachments and formations available in the Fall of Cadia. This is going to be awesome!
They have a few details on the Triumvirate, Mars United (Not a football team), and Crusade for Cadia. The Adeptus Mechanicus formations allows you to form detachments from Cult Mechanicus, Skitarii and Imperial Knights into a combined single army, apparently, and features power of the machine spirit. Wait, that's the Grand Convocation we're talking about here. The other formation, the Conclave Acquisitorius is a super big formation that grants all the characters master-crafted weapons and I think free relics and wargear (I could be wrong). Grand Convocation is a more flexible choice that allows you to mix and match, while Conclave Acquisitorius is more rigid, but allows your Mechanicus forces to grant each other a mix of abilities from all the armies. Or something. We shall see.
On the other hand, we have the Wrathful Crusade, which combines the Black Templars, Astra Militarum (Imperial Guard, jeez), and Adepta Sororitas (Sisters of Battle), all of whom are led by Celestine and Inquisitor Katarina Greyfax. It's a troops-heavy formation, apparently, but the awesome part is that everyone gains Hatred AND you can bring Troops back from the dead, just like the Lost and the Damned from the Traitor's Hatred thing. I think. I can't remember (sorry, I'm not a Chaos player). For the Emperor!
Adeptus Mechanicus and Astra Militarum/Imperial Guard "Wiki"
Incidentally, my blog also serves as a sort of "Wiki" for the Mechanicum during the time of the Horus Heresy (30K), the Adeptus Mechanicus and to a smaller extent, the Imperial Knights and the Imperial Guard...I mean Astra Militarum. I will endeavor to expand and construct new posts and articles on them. Feel free to comment, criticize and advise changes in the comments.
These posts will be about fluff, unit analysis and "tactics" similar to that of 1d4chan, but obviously I suck at it, being an amateur, so go read 1d4chan instead. But in the fluff sections for the 40K articles, I will include my own personal fluff regarding the Draconis system such as the Knight House Yato in Draconis III, the Astra Militarum regiment trained there, the Draconian Armored Defense Force, and the Forge World of Draconis IV with its Mechanicus priesthood and Skitarii legions, and perhaps the Titan Legion, Legio Gojira.
Skitarii Tactics (under construction)
Cult Mechanicus Tactics (under construction)
Astra Militarum/Imperial Guard
Astra Militarum/Imperial Guard Tactics (under construction)