Miquella is the most likely candidate for a DLC. He's the only Demi-God we don't meet aside from Godwyn (and even then, we at least see Godwyn's body) and is all too important to the lore. The guy had possibly found a solution to replace the Edtree and save the LB on its own and he's tied to Malenia (of course) but also Godwyn, Radagon, Marika and (if the theory about Malenia going to Caelid because she somehow learned Miquella was somewhere near the place, even if she was wrong in the end, is true) possibly Radahn, he's way too important to simply remain a background character with that amount of lore. So if DLC there is, it will either be about Miquella or Godwyn. That, or we will get the usual time travel stuff. About the dream stuff, we do enter Godwyn's dream to fight Fortissax so it's a genuine possibility.
I also think there's a genuine possibility we would get more stuff about Rykard. Like, he's the ONLY character in the game outside of Malenia and to a degree Millicent with heavy implications that he's either still alive or will return one way or another. It's particulary notable since not only his whole character is about immortality and his serpentine motif is tied to rebirth, his dialogue starting after the "Great Enemy Felled" message is all too remarkable. I love the guy so I hope we'll get more of him. Also, I wish we could have more about Mohg. He's quite frankly my favorite character in the game and while he does have a great boss fight, design, OST, personnality, etc, he should have had much more. It's a shame the quest and the additional dialogue he had were cut so I wish we'll have more of him.
Aside from those, Kale had a whole quest for himself tied to the Frenzied Flame and Vyke also had something about him apparently. Considering the lore of the character, he could have had more. I also kind of want a time travelling DLC (well, kind of). I hope we'll get more of an insight to the war with the Giants or Marika.