Curious they didn't figure out how to do it when they added Vlad to give him Isabella as a secondary unit and have some enrage mode when she dies(and if they share hp she'd die at say 50%).
As for the story thing, not new factions, no alternate mini campaign like Beastmen, it's just new LLs so they have their own quests like every LL and starting point with a few unique campaign mechanics(like how you can't recruit Orcs right away when you play Skarsnik). But it's still mostly just a Dwarfs or Greenskins campaign.
The new "story" stuff will be next DLC probably, when they release Wood elves. Or Skavens. Or both. There's a bunch of Skaven teasers in that announcement(the coins on the page have the skaven banner triangle on it and one of upgrade in Eight Peaks for dwarves mention Rat Poison to keep away human-sized vermin), which is curious since Wood Elves should have been first, and might still be, I guess we'll see.
Reddit detectives say Wood Elves were supposed to be this DLC but they might have fallen behind so they pushed this one up instead, so we get 2 LL+RoR DLC in a row instead of LL+RoR > Wood Elves > LL+RoR 2 > Skaven.