I heard that it was the opposite, that it was a physical limitation, due to the larger AF sensors and not something that could be fixed with a firmware update. However, it was just the opinion of a CPS rep and he didn't have any hard evidence and hadn't been told anything beyond how the system worked and he admitted that he could be wrong.
It is a physical limitation. AF sensors are all about angles, and the exit pupil for an f/8 lens will be invisible to AF sensors that are aimed at the f/5.6 or larger exit pupil. I don't think firmware will change this, unless they update it to ignore the aperture and tell people that it may or may not work. That's what happens with the pin-taping that people do. Sometimes a bit of light bleeds around enough for the sensor to grab onto -- though I wouldn't call it reliable.
Live View could be an option for a lot of uses, though.