Bad news from the Radio 3 message boards.
Quoting an email received by one poster from the BBC:
(20 November 2006 11:13)
Thank you for your interest in Radio 3. We really appreciate all feedback from our listeners and so it is good of you to take the time and trouble to write. It is true that Mixing It will not appear in the new schedule, but we have not yet announced all the changes and some of the press reporting of the changes has been inaccurate. I do hope that you will find much to enjoy on Radio 3 and that you will continue to give us feedback once the new schedule is in place.
With best wishes
BBC Radio 3
Update (12 Feb 2007): following the final Mixing It broadcast, Mark Russell has posted a few words to his site explaining the story as he sees it. They make sad reading. (thanks to commentor sig for the heads up)