It's emergency exits that are the biggest problem. Someone sitting in the middle of the aircraft could be a long distance from any emergency exit. Putting some in the floor wouldn't help if the landing gear is destroyed, and the plane is resting on the bottom of the fuselage. There's also a problem with excessive G forces in the seats furthest from the centerline of the aircraft that could make the ride uncomfortable. That's the main reason they're talking about this being a freighter, but even then it would be non-live freight. I don't think race horse owners would want their expensive horses subjected to excessive G forces away from the centerline.
Where the 747F(reighter) Trounces the A380F is (despite the higher volume of the WhaleJet) is that it's 1 main cargo floor is very strongly supported for heavier loads in very dense capacity.
Whereas, the A380F, though possessing 2 cargo floors, is not designed for dense weights so it can only carry lighter yet bulky items such as FEDEX, DHL, UPS, etc. do.