This is sorta pseudo fluffy and also a gigantic wall of text, you have been warned.
I have been reading The Inquisition War since Christmas (I'm usually much faster when I don't have school going on). It brings a lot of interesting ideas and sort of fluff theories. Also reading Just_me's wonderful article on the Emperor a few days ago inspired me.
I love Tzeentch, and Nurgle too to a lesser degree, the fluff the formerly loyalist legion how/why they fell, etc. I connect to it a lot. A lot of CSM players/fans and I guess more broadly anyone who is remotely interested in Chaos sort of have "their God." Some people LOVE Khorne and Slaanesh, they don't do a thing for me. Nothing, nada. But I really get Tzeentch. The desire to control, to hold forbidden knowledge, the mastery of powers others cannot comprehend. Hook, line, and sinker.
With reading Index Astartes, various other codices, and sources a (possibly) radical thought has emerged. What if all Chaos is the Lord of Change?
In older fluff (specifically The Inquisition War) it either implies or states that the Emperor's mind has become fragmented, often warring with itself through the various parts of personality now each made manifest as an individual voice. A deity with Multiple Personality Disorder. Cannon has it that Khorne was the first of the Chaos Gods to fully awaken. As each of the 4 (major) dieties makes up Chaos as a whole, couldn't they be the fragmented personalities of a whole? As Chaos was congealing different parts of the persona awakened, Khorne as rage/anger/hate, Slaanesh as excess/hedonism/pleasure, Nurgle as despair/stagnation/disease, and Tzeentch as change/knowledge/magic.
We could also then suppose that the Chaos God with the greatest emphasis of knowledge and ambition make up the greatest plurality, and therefore consciousness, of this evil gestalt. In the same way that the Eldar are hoping to form Ynnead, might the Great Schemer be plotting to become a singular evil deity?
I would like to challenge the assertion that Tzeentch "can never win." If the Changer of Ways ascended to the top (regardless of the absorption of the others to form one mega-evil) he would still be able to manipulate every being beneath him. There would still be ambition, backstabbing, and beings trying to claw their way to the top. Something like an infinitely vast corporate ladder that no one could truly hope to finish climbing. Their would still be the hope and drive to ascend by the Great Conspirator's puppets. He may even let a few of them come close to succeeding for amusement. Pages 152-153 of the BRB gives one of my favorite stories about Tzeentch and his manipulation of his antithetical brothers.
Diametric opposites abound in 40k. Chaos is the malevolent reflection of life in the Warp, with the Emperor generally seen as the embodiment of good (though he is not without flaw, due to inaction or other means). The C'tan are in many ways the evil opposite of Chaos. They abhor the warp, but still seek to keep all life in the universe under their heel. Each has their own agenda as well as a horde of followers. There's 4 C'Tan left. Technology vs. magic. Called Star Gods, etc etc etc. Though all of that is a discussion for another time. So could not this point to Tzeentch as the most direct opposite of the Emperor, and lead to a path that would only see Tzeentch (and therefore Chaos) ascending to its rightful place and finally shackling the galaxy once and for all?
To steal something from a great Edward Norton film, I'm going to end with a quote (from Codex: Daemons)
"Don't you see? My Master Tzeentch cares not which of the Great Powers of Chaos you serve.
In the end, aren't the followers of the Blood God changing valiant warriors into headless corpses? Aren't the worshipers of the Lord of Flies changing strong, healthy bodies into rotting, diseased carcasses? Aren't the disciples of the Dark Prince changing stern, steadfast heroes into slaves to their own senses?
Chaos is a struggle to change, you must agree. Change rules all."
TL;DR Tzeentch > all
Thanks to those that somehow managed to read all of that. I'd love to hear what anyone thought.