Max and Beata and Ricardo and Yulia are definitely doing it as they told my friend in Blackpool. Sergey and Melia are definitely doing it as they told me they were, as did Bryan and Carmen.
I think Michael and Joanna are obviously going to be there and that Peter and Kristina are also pretty sure to be.
I don't know who a seventh couple would be if that is true, but I would suspect Michael and Hidemi are likely as I'm sure they would love for a Japanese couple to do it. Also back in 2005 they asked Michael and Tebogo before they even danced any competitions.
Or perhaps as said before it could be Franco and Oxana. I for one would really enjoy to watch their show, if so!