That's really early for a cast announcement. Especially since the show doesn't debut until September! I wonder if they're afraid of the cast leaking out way ahead of time.
I wouldn't be at all surprised (or disappointed) for Carson to return. Meh to Tia and Dmitry, if that has anything to do with them possibly being on AS. Hopefully they give Dmitry a partner with personality so he doesn't fade into the woodwork for me if he's back.