A bit of a lengthy post here so let's dive right in, I'll organize my speculations off by what I believe to be most obvious/ feasible by CA at this given time, not in the order I expect them to be released.
First, I believe Tomb Kings is the most likely DLC to enter WH2. Both the Vortex map and Mortal Empires map have the perfect slots to fit them in, at this point we're basically just waiting for the trailer.
Secondly, Vampire Coast, I think this will be like what they did with Bretonia, where they will be FLC towards the end of year 2 content and give them a full roster with lords and unique campaign mechanics.
Not 100% sure how this faction will operate, I was thinking they could work similar to black-arks with a bit of Beastmen/ Warriors of chaos thrown in. All their military buildings will be built on their ships and essentially become their settlements, but the military buildings are only availible while on the ship as well as resupplying your troops. Majority of the economy will come from raiding coastal villages, the Vampire Coast itself is where the death fleet will be built so you'll have to keep a presence in that area at all times. they'd never suffer attrition at sea unless in a reef or whirlpool area.
Thirdly, Araby is the next one I believe that could be possible. My only concern regarding Araby is their proximity to the Tomb Kings, inevitably they'd go to war and one race will be wiped out before any other race could encounter them, along with Tomb Kings being a favorite among fans I believe CA would rather have them grow to become a chaos invasion type enemy in the game with Nagash
-Dogs of war
This one I haven’t put much thought to because I’m unsure how they’d even operate, they do have a large fan base so I could see CA consider them though.
I believe they’d work very similar to rogue army’s and maybe even be able to confederate other rogue armies. As to how they’d recruit/ build once again I haven’t personally considered them to be a DLC but I know Ineptgeneral is currently making a 3part series about them, so if you’re curious about that look at his channel.
Next few are exceptionally speculative so bare with me.
With this DLC we'd see naval battles introduced.
Sartosa, they'd work very much like the Vampire coast except they'd be able to build settlements along the coasts like Norsca. they'd start the game with fog of war lifted off all coastal regions as they are a massive pirate operation, and they'd gain a profit from any factions that set up a trade agreement that goes overseas. they'd also be able to raid enter raid position at sea and gain extra loot in regions where the ocean is not controlled by them.
The only issue with Sartosa is I'm not sure how the military would work, perhaps like a rogue army where it's many different factions put together to make up a balanced army.
the main reason I'm not certain of this one is that Sartosa doesn't appear to be on the Mortal Empires map or that they'd have much to do with the vortex campaign, to begin with.
Albion could be very interesting in that they'd almost constantly be under attack from chaos invasions, Albion is home to a rock circle that reinforces the great vortex and would draw the attention of chaos. so, they'd make sense for the great vortex campaign. however, like Sartosa, they don't appear on the Mortal Empires Campaign. Another thing that could make Albion unique would be that the old ones created a race of giants to guard the island, Bologs is supposed to be the biggest strongest Giant of them all and is literally worshipped as a god, I think he'd make an interesting legendary lord. They'd also be great to compete with the Norscans for Norsca because up to now nobody but Norscans can settle there.
Dreadfleet would be more of an add on for all the races. It’d introduce a new chaos invasion type enemy with Count Noctilus sailing around the sea’s razing every settlement he came across, I think it’d be interesting if he started in the North near Naggaroth hassling all Elven kind before moving on to Lustria and the old world. He’d most likely have a very similar Army to what Vampire counts already have but even making him part of Vampire coast DLC would be perfect.
But more importantly, it’d introduce naval combat and a new legendary lord type in Legendary Admirals. They’d work much like any other legendary lord but can only take part in battles at sea, in the Dreadfleet lore most races were represented and had unique ships, it wouldn’t be hard to create new ones for those that weren’t in the story though.
The Legendary Admirals would have their own quests and perk chain along with abilities and buffs/ debuffs. This they could really get creative with as the ocean could be a very crazy place within the Warhammer world.
These ones I consider unlikely.
Like Sartosa, Amazons don't appear on the map, in fact, Amazon island in general, isn't even on the map and I don't feel CA would be able to add a land mass that could work very well for them.
-Chaos Dwarves, Daemons of Chaos, Ogre Kingdoms
Those guys are reserved for Warhammer 3 so don’t get your hopes up for them at this time.
As a closing statement I hope that CA doesn’t stick to the Old-world formula of only two DLC race packs then an FLC pack then move on to the next game. I’m more than happy to pay for quality content and would love to see more added to this awesome game and expand its replayability.