One reason Boeing dropped the two deck option was it ended up costing too much in terms of added weight for the second floor. I've seen the same comment repeated by other designers. (Douglas and others looked at this at various times)
It would be interesting to see the take off weight per seat of the 747 vs the A380 vs say 777 or 340. Need to use the same fuel uplift for a chosen range.
Also re flight deck crew - will the A380 be a 2 or 3 body operation (Not considering relief crew)
The problem I see is that unless you fill all those seats - every empty seat is making any seat mile advantage go bye bye very quick.