Slaanesh would fit into the Vortex well, with N'Kari and Dechala The Denied One both tying in to the Dark Elves and High Elves. They'd then reappear in the Chaos Wastes in game three, while in Mortal Empires one would go to the wastes, with the latter staying in Naggaroth.
Kislev would start with Tsar Boris Bokha off in the farside colonies of the Kislev Wheatlands. Specifically the settlement of Chernozavstra, trying to maintain those new areas against a zombie plague that's swept through. He'd have abdicated the rule of Kislev to his daughter, Tsarina Katarin, who starts dealing with the Boyar Traitors who have risen up due to the extreme costs they've incurred from all of Boris' reforms and expansions. FLC/DLC would be Tsar Saltan of Praag, and Prince Ivan Radinov, off exploring in some far flung corner of the map.
Daemons of Chaos would start with U'Zhul the Skulltaker and Epidemius the Tallyman, battling with N'Kari's forces and Norscan warlords over control of the Chaos Wastes. The Changeling and the Masque would join in the fun at a later date.
Chaos Dwarfs would start with Zhatan the Black, forced to take care of Kislev colonists up around Uzkulak and Drazhoath the Ashen in the Black Tower driving off some Ogres. Additions would be Astragoth Ironhand in Zharr-Naggrund subjugating a Greenskin revolt, and the traitor Todrek Hackhart reclaiming his home of Barak Varr.
Ogre Kingdoms would start with Skrag the Slaughterer out to feed the Great Maw, and Golfag Maneater doing some work in the western Dark Lands. Later, Greassus Goldtooth would have to be rolled out of his hall to take on the Southern Realms armies trying to wrest control of the Ivroy Road from him, while Braugh Slavelord would bring his soul-binding chains and a little death magic to spice up things on a slave-raid in the west.
Ku'gath Plaguefather and Tamurkhan would have control of the Chaos Divided forces of Nurgle, while Khorne would get Skarbrand and Valkya, and Tzeentch forces would be led by Kairos Fateweaver and Egrimm van Horstmann.
As the Chaos Divided forces came out, Warriors of Chaos and Beastmen would get the respective marks as FLC.
Story would revolve around two main points: securing trade routes, and building favour with the gods.