WMG / Horus Heresy

Chaos Gods managed to hack Acuity
The Acuity felt that the simplest solution was Kill 'em All
  • Or the Cabal wants to see both Chaos and upstart humanity dead.
Alpha Legion WMGS
  • Alpharius want to use the stolen genetic sample to become the Emperor/clone him
    • Alpharius is the real Primarch of the Grey Knights.
  • Omegon fell to Chaos
Mechanicus "dragon cults" will turn on Horus sometime later
  • Are those a thing? The Dark Mechanicus is unstable as it is.
Emperor's Jerkass attitude was intentional in order to led to Horus Heresy
  • Emperor could understand people and treat them well - remember Vulkan and Kai Zulane. We know his Well-Intentioned Extremist character well. So, how could be so stupid? Another interpretation may be that he in fact rebuked Lorgar to inspire his treachery, saved Angron while leaving his comrades to die, withdraw knowledge of Chaos, etc. Add the fact that Iacton Cruze is the friend of Cypher, and killed a loyalist guard, possibly to provoke Dark Angels into falling.
Revuel Arvida will somehow create the Blood Ravens
  • Pretty much all his appearances, but especially the Rebirth short story, practically telegraph a connection. His pre-Heresy Thousand Sons armor colors are a dead ringer for the Ravens' colors, the emblem of the Corvidae could easily be distorted over time into the Ravens' symbol, and he outright quotes half of their motto. Add in the Blood Ravens being known for a relative abundance of Librarians, a trait which they share with the Sons, and it's almost certain that the writers are pushing a connection. As for how it's possible, Revuel wasn't the only Son sent away from Prospero before the Space Wolves arrived. It's possible he will gather his scattered loyalist brothers and rebrand them to conceal their traitorous heritage until the knowledge is lost entirely, resulting in the current situation where the Ravens have no idea who their Primarch is or what their origins are.
http://tvtropes.org/pmwiki/pmwiki.php/WMG/HorusHeresy