His next one is supposed to be on 5-point match cubes and has a target release date of April 2023 (past) on his website. I was wondering if anyone had updated information (I believe he was behind estimated on his others too).
His books are among my favorites and I am very much looking forward to his explanation on this topic in particular. 
He told me earlier this year that it should be around the end of this year, but I haven’t heard any update since…
I know too optimistic schedules quite well 
So, update! On the Chicago ABT stream, Bill Riles asked Michy when his next book would be out. Michy said (pretty confidently) this November, but also that he will be busy (getting it ready?) between now and then. 
Also, I believe this seminar (currently waiting for upload) is on the planned book's topic:
Cube Action in a Five Point Backgammon Match - Seminar by Michihito Kageyama