There is a discussion on this topic over in the DL forum. This is a different topic than the merger topics - since the DL/NW full merger has failed but a light merger (a la AF/KL) is going to take place.
As discussed before - CO is really the odd one in SkyTeam. With this new competitive force - SkyTeam offers nothing to CO other than FF plan benefits. CO is in SkyTeam because Wings Alliance failed and really no place else to go.