I prefer to use DMF with both the A9 and A7RII. Cause I can "read" (feed back) where the focus is with the peaking display.
But I would like to have the camera to automatically switch to AFc when I press a dedicated Eye-AF button, so that the camera keep tracking the eye when I want. And return to DMF (or any other AF mode) when I release the button.
So it would great to have an Eye-AFc mode, in addition to the existing Eye-AF.
Very simple to implement I think, for future firmware releases.