There've been no official Dickensian casting announcements yet, but word about casting is starting to leak out via actors' Twitter accounts. So I don't think anyone will object if I mention that Caroline Quentin is playing Mrs. Bumble, and Sophie Simnett is playing someone's niece. (Whose niece, I don't know. She looks a bit young for Scrooge's niece.) Additionally, this site lists Stephen Rae as a cast member, though with no role given.
It isn't much, but it's a start -- and I'll let you know if I find more!