MEM will be the last of Fedex' worries. Fedex has so much clout with the airport & the city, that the MEM upgrades (if any) will happen in time.
The issue for Fedex may be less-willing airport authorities at some other A380-possible airports such as IND, EWR, MIA, LAX, or OAK, not to mention the off-shore airports.
I dumped at the gybe mark in strong winds when I looked up at a Porter Q400 on finals. Can't stop spotting.