If she's going to do anything then it would need to be done very soon (while Lindsey is releasing/touring his new record ahead of the next FM tour). I don't think Christine has it in her to be the prime driver behind a blues record but if Mick wanted to do something with Rick then I'm sure he could push things through with Christine also involved.
I don't see her realistically doing anything more after a 2 year world tour. She is looking quite frail.
Edit: I'm not sure frail is quite the right term, but certainly her best performing days are long, long gone.
'Where words fail, music speaks'