Let’s try to design a fun to play Chaos faction, while being different from the other races.
Chaos has four doctrine slots, one of which can only be filled by a Worship Doctrine, though you can also fill one regular doctrine slot with another Worship Doctrine, bringing the number of Worship Doctrine to a maximum of two out of four doctrines.
Worship Doctrines unlock new units, researches, and give access to unique elites aligned to a deity of Chaos. There are four Worship Doctrines, one for each major deity of Chaos, so Khorne, Nurgle, Tzeentch, or Slaanesh. According to which Worship Doctrines you’ve equipped your Cultists will also have access to different Worships.
Cultists have the ability to Worship the Chaos Gods, it depends on which Worship Doctrines you’ve equipped. Worshipping is similar to DoW2, and gives buffs/debuffs but disables actions when activated. Khorne increases the speed of nearby units, Nurgle allows health regeneration, Tzeentch infiltrates nearby units, and Slaanesh slows nearby enemy units.
Ultimate – Warp Rift
Create a Warp Rift (visually similar to that), which deals light damage and allows the production of Chaos Daemons for a reduced cost from the Warp Rift itself.
Desecrated Stronghold (produces warp smith (builder) and cultists), Chaos Temple (produces infantry), Chaos Armoury (researches), Machine Pit (produces vehicles and warp smith (builders)), and Daemon Pit (produces daemons).