If you do not press anything on the camera you will not get any AF confirmation. And for me the reason is sample: the camera processor do not get anything from focusing subsystem.

But if you halfpress the shutter or press the back button (if you use back focus button) you will get confirmation (tested with EOS 5D MIII, same lens, w/o extender). And the reason is focusing subsystem is activated and processor receive signals and can get when the focusing point(s) get the focus.

I do not have information what will happen with extender (x2) because the resulting aperture will be beyond F8 but IMHO this is limitation of autofocus, not focus confirmation so you will get it.

Short: Yes, IMHO you will get focus confirmation.

Long: If you do not press anything on the camera you will not get any AF confirmation. And for me the reason is sample: the camera processor do not get anything from focusing subsystem.

But if you halfpress the shutter or press the back button (if you use back focus button) you will get confirmation (tested with EOS 5D MIII, same lens, w/o extender). And the reason is focusing subsystem is activated and processor receive signals and can get when the focusing point(s) get the focus.

I do not have information what will happen with extender (x2) because the resulting aperture will be beyond F8 but IMHO this is limitation of autofocus, not focus confirmation so you will get it.