Yeah, the endocrine role in signaling has been left out for quite some time. In the 80's mitochondrial research was in fashion and then the idea was getting interest until DNA sequencing became possible. About their role as HDAC inhibitors, I'm not sure it's a big player.
What is most likely is that in some individual populations of cells any source of energy for the mitochondrial like ketones or any other metabolite in the Krebs cycle like acetate could extend mitochondrial activity and thus indirectly longevity.