Thanks all! Good to know my idea of a "cheaper" Sons of Horus force is reasonable
@darkhorse: You know, I never saw that image so I looked it up and...
Yeah. That's easily like the new Chaos Marines
I think the styling of the Sons of Horus is intended to be the source of the aesthetics of chaos marines and that it is just a stylised progression that was adopted by all Traitor Legions as a whole so entirely plausible. Even little bits like the traditional chaos Anvilus pattern backpacks have been adapted in the lore to justify their evolution. In this case being a prototype backpack developed by the Forgeworld Anvilus in the later stages of the Great Crusade. Anvilus was captured by the Traitors early on in the Horus Heresy and was used to arm them throughout the conflict. Add these to the style of the SoH with all the spikes and hard sharp angles and you basically have proto chaos armour.