I'm fairly certain Shani has been hinted at being in one of the expansions. I was personally hoping I'd run into her on Triss' missions, with Shani helping the mages out. I thought that'd be a lovely way to see the two women getting over their past issues, be good character development, and having an implicit (but not overly obvious) feminist message {we can still be friends/colleagues even though we once fought over a man}.
I'm fairly certain a lot of Witcher 2 characters will be in at least one of the expansion pacts, but I hope they focus on the first Witcher's characters as well. I would love to be given the option to determine what side I picked in the first Witcher, and then to run into the characters of that side latter, for instance.