A single line of advisor dialogue datamined from Total War: Warhammer 3 (opens in new tab) has all but confirmed that the next faction coming to Creative Assembly's masterpiece (opens in new tab) is the expected one: Chaos Dwarfs.
"Exercise caution, my lord, for your scouts bring word of Chaos Dwarfs nearby. The Legion of Azgorh are a callous and black-hearted foe, bearing little resemblance to their untainted cousins to the west. Keep your weapons close at hand," says the gritty voice of the advisor in a short dialogue line posted to YouTube (opens in new tab). It's reminiscent of the lines the advisor says for encountering almost any other major faction during the campaign.
With their settlements currently occupied by black orcs, but sitting at the very center of Warhammer 3's campaign map, it was already widely believed that the Chaos Dwarfs would show up sooner rather than later. This line of dialogue all but confirms it.
To take a quick Warhammer Fantasy lore nerd side trip, the voice line references the Legion of Azgorh. That's specifically the band of Chaos Dwarf criminals and exiles charged with defending an awful forsaken border fortress. They're led by Drazhoath the Ashen, a sorcerer-prophet who rides on a giant fire-breathing winged bull—so he's a shoe-in for one of their legendary lord choices.
Otherwise, expect lots of demon-infused artillery cannons and extremely heavily armored Infernal Guard soldiers wielding greataxes that are also repeating rifles. Should be a blast, especially if they put in the daemon-fueled steam locomotive covered in cannons. (opens in new tab)