So there's a free PDF for a scenario for the Horus Heresy called the The Burning of Ohm-Mat that strongly suggests that there may be to 8 Chaos Gods in the future (or at least are winks-and-nods at prior things like Malal).
Granted, this was during the time where Daemons and The Warp weren't strongly understood, but you could pick one of these for each unit of Daemons:
The main four are obvious the ones we know - Heedless Slaughter (Khorne), Infernal Tempest (Tzeentch), Putrid Corruption (Nurgle) and Rapturous Sensation (Slaanesh) but the others, as described:
Encroaching Ruin: "Chaos in its purest form is a terror that few can stand before and remain sane. It hungers only for destruction, that all things mortal meet their predestined end and crumble into dust to be forgotten. To this singular end it moves inexorably, driven by a nightmarish purpose which subsumes the petty divisions of daemonkind."
This would be The Great Horned Rat in AOS, and The Dark King in 40k
Malevolent Artifice: "Just as Chaos reflects back a twisted mockery of humanity’s every facet, so too is the very drive to create perverted into a malevolent and destructive force within the Immaterium. Conjured forth into realspace, such daemonkind harnessed the works of mortals as a vector for their own annihilation, their monstrous machine-entity forms at once a mimicry of flesh and artifice, every action made to demonstrate their supremacy over both mortal beings and everything they deigned to create."
Hashut (AOS), Vashttor (40k)
Ravenous Dissolution: "Such is the hatred that swirls within the Warp that it encompasses all things, and like the dragon of eternity that feasts upon its own tail, this hatred extends even to itself. To expect rational and sane logic from creatures such as these would be foolish, for Chaos was both its name and nature. Yet, in its self-destructive hatred there was no ally to be found, only a new and more unpredictable foe."
Necoho/Zuvassin (AOS), Malice/Malal (40k)
Formless Distortion: "Even as Daemons manifest as obscene parodies of mortal forms, the true essence of Chaos is endlessly shifting and unknowable, twisting, changing and perverting everything it touches. Some Daemons who crossed the veil into realspace embodied this ceaseless distortion to its fullest extent, shaping themselves into roiling agglomerations of immaterial flesh and bone, for whom death was simply one component of the eternal metamorphosis they would inflict upon the material world."
Morghur (AOS), Unknown (40k)
Tagging you Jax @skxrbrand because I know you'll appreciate it!
