I liked Shani and in my playthrough Geralt was in a relationship with her (writing a letter to her was touching and hilarious at the same time). But I don't think she can really serve a main role in Witcher games, especially considering she was a fairly minor character in the books (or so I've heard). It would be nice if she was mentioned at least if you ended up choosing her over Triss, but I don't see the need for anything beyond that.
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It is strange that Shani hasn't been annouced yet (strange, that is, if Shani is intended to be in the final release), but as they have two more characters to show, she still might be in.
And you are right that she doesn't play a big part in the books, but, frankly, the books don't play all that big of a role in the first game, and probably won't in the second. The people who play the games and the people who read the books are two different types of people.
The Triss or Shani choice in TW1 was mostly cosmetic - the game played out almost exactly the same way regardless of you picked. The only thing it really changed is which of the two is featured in the second half of the game.
I actually preferred Shain myself, but Triss does make more sense.
I always went with Shani. She made for a better mom and I thought she was hella cute =) I really hope she makes some kind of return in AoK though. CD Projekt Red said that you could carry data from the first game over to the second one, so I'm really curious to see what happens in the second game if you went with Shani in the first one.
"Empires do not suffer emptiness of purpose at the time of their creation. It is when they have become established that aims are lost and replaced by vague ritual." -Muad'dib