No idea. But I think that they might implement new weapons(Something to replace the crossbow), like throwing knives, etc. I also have a feeling that it will have a lot of little easter eggs and remarks, making fun of lord of the rings(long time coming) and Star Wars, like in Hearts of Stone, where the Caretaker felt like he came straight from bloodborne.
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Though, i hope there will be:
More Witcher lore(with more of the witcher characters), to explain things better.
More of Zoltan Chivay, Dandelion, Priscilla(with a new beautiful ballad, of course) and Vimme Vivaldi.
Also, I REALLY would like to know more about that talking cat and dog found in and around the Von Everec's household.
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I may be asking a bit much now, but who knows? Maybe one of my wishes will come true.
OH, and one more thing. I believe that toussiant will be introduced like a holiday resort, where some characters from
the main story will go to have a break.