Well AF has always been firmware limited, this can be proven quite easily with a none reporting TC.
a camera can attempt to AF at any aperture if it really wanted too. However with smaller apertures it would probably be unlikely to succeed unless you were focusing on the sun at noon.
Now for the 1Dx it would most likely be limited by Firmware, therefore accuracy probably won't be any better than before the firmware change. However how accurate was previous 1D at f/8?
I don't think canon was being dishonest mearly that they felt that accuracy at f/8 was not good enough for there standards.
Obviously it was a firmware fix. I think KCY was spot on with this sentence ^
I was happy before, and I'm even happier now