Apparently the biggest problem for double-deck passenger aircraft is the need for customized jetway bridges to access the plane.
It takes 45 minutes to load an A380 using two jetway bridges to its lower deck; adding a third bridge to the upper deck reduces that time to a little over a half hour.
I seem to recall that the Japanese were asking Boeing for a triple-deck 747. The idea they were perusing was a short haul, high capacity commuter plane to speed up inter-island transportation.
The proposed layout would extend the first class lounge all the way back to the rudder, and the cargo deck would be converted to a carry passengers as well.
I don't know if Boeing talked them out of it or the Japanese rethought the logistics of embarking/debarking passengers by the thousand lot, needles to say it "never got off the ground!"
Regards,
GtG
IIRC most of the world's most important airports have already modified their operations to accommodate it.There are already a half dozen in the US that have adapted and they say that even Boston will be getting 380s next year.If Boston is added can Minneapolis be far behind? Add a number of European,Asian and Australian airports to the list and this doesn't seem to be the issue it might have been 5 years ago.