Knowing Mick if this was going to happen, he'd have said so already... "THE MAC IS BACK WITH CHRISTINE!"
That said... maybe they are using Christine to get Stevie onboard with a new album... or maybe they are trying to get her involved in a record...? God knows.
It is unusual that she's traveling to see them, considering she hates to do so. We could guess about it all day... but the fact that Mick even mentioned it to begin with surely says
something.