The core races in WH3 are the 4 seperate Monogods, Kislev, Cathay and perhaps also Undivided Daemons of Chaos, if Be'lakor being 9th lord is any indication. 1 more race will join in the form of pre-order, most likely Ogre Kingdoms, Dogs of War or Chaos Dwarfs. That still leaves 2 major racepacks for WH3 down the road and 2, during its roughly 4 year lifecycle, was what WH2 recieved in the form of the Tomb Kings and Vampire Coast. WH3 will likely last longer, so perhaps its best to think in terms of 3 major race packs, MAYBE 4, by trilogy's end. 2 of those would likely be the aforementioned Chaos Dwarfs and Dogs of War.
After these, would stand fan-favourite Nagash and his Undead Legion, but here we encounter difficulties depending on what route CA decides to take WH3. Not only would it be a question of which lords to include, but also, there is the matter of the minor races of the WH3 setting: Ind, Nippon, Khuresh and even in the distance, the Kurgan. If CA decides to include either Ind, Nippon or Khuresh as seperate unplayable civilzations on launch, then there is a good bet that they are planning to make them playable at some point during WH3's lifecycle. Then, with only 1 or 2 spots open, it would be a matter of priority whether to focus on entirely new factions, or on the Tomb King-Vampire clone that would be Nagash's Undead Legions.
As for the Legion itself, who would be its lords besides Nagash? As things stand right now, that's not an easy question to answer. His mortarchs are largely taken by other factions, with Vlad and Manfred in Sylvania, Krell a summon by Kemmler, Arkhan the Black hanging out in Nehekhara and Luthor Harkon in Lustria. Neferata is likely to be taken too, becoming head of the Lahmians in Silver Pinnacle at some point during WH3. With that, all the major titled-Mortarchs are taken, leaving us barely with 3 characters. I say 3, as I suspect that CA won't accept other WH videogames as established lores, which would eliminate the 3 mortarchs (Dread King, Virion the Grim and Hand of Nagash) appearing in Warhammer: Dark Omen who are not mentioned anywhere else. That leaves Dieter Helsnicht, Walach Harkon and Constant Drachenfels AKA the Nameless. A less powerful Necromancer, a Blood Dragon Knight and a spirit without physical form, other than perhaps the possessed body of Luthor Huss? Is this the ideal version of what Nagash's Legion would be represented as?
What of starting positions, besides Nagashizzar? There is no easy answer here either. Walach Harkon and the Nameless would've been easy to place in Blood Keep and Castle Drachenfels, if it weren't for the fact that Skarsnik and Heinrich Kemmler are both blocking any further access to the Grey Mountains. Dieter Helsnicht is in a better place, but his Forest of Shadows hideout will likely be occupied by Zacharias the Everliving and the Necrarchs, assuming all Count lines will be playable at some point. With no obvious starting locations, would it be better to have a one-man race, coming in a regular LP rather than a race-pack, operating solely out of Nagashizzar, perhaps with remaining mortarchs as simple recruitable LLs?
Or perhaps a different scenario entirely, with no Nagash race entirely? If Neferata is placed in charge of Silver Pinnacle in WH3, perhaps her campaign goal could be to go down south and conquer Nagashizzar and perform a great ritual to bring back Nagash? Who would she conquer it from? Well from the Skaven, as Nagash did in the lore, perhaps from Skreech Verminking himself as a possible 8th lord for the Skaven after Thanquol. This would symbolize the united Skaven clans who destroyed Nagash the first time.
What do you think guys? How should Nagash be handled? A full 4-lord race-pack, a one-man race or a campaign goal for Neferata in WH3?