Arash -
I agree that to me AF on the new MK4 will be a key feature
But i'm not convinced that you're argument is correct
If you look at the more "sensitive" cross-type AF points on the new MK4, not much has changed from the Mk3 for those that use f4 L lenses. Here's a link that addresses the issue:
http://cameragossip.blogspot.com/200...af-module.html
All the improved AF features on the Mk 4 really only apply to use with f2.8 lenses. So those using the 300mm or 400mm f2.8L will likely be very happy with the Mk4.
The 7D has all 19 AF points function as cross-type AF sensors up to len combo's of f5.6 (ie- a f4L lens x 1.4 TC). I think many who have both the 7D and Mk 3 will privately admit that the 7D has superior AF for BIF. Most AF sensors on the high-end Nikons are also cross-type AF sensors up to at least f5.6
There are many great-looking features on the Mk4, but i'm not sure that improved AF with an f4 L lens will be one of them.