I can't see airports in the middle of the US making the modifications. DFW doesn't currently have any 747 passenger service. I don't think IAH will make any modifications for the A380 either, and both airports were built to accomodate the 747. IAH opened about a year before the first 747 entered revenue service, and DFW opened about three and a half years after the 747 came into service with the airlines. Both airports were built with much room for expansion unlike most other airports in the US. Airlines at IAH are more interested in having multiple departure times to allow more flexibility for their business customers than having one big plane that arrives and departs once every day. I'm sure DFW would just be happy to get one 767 or 777 flight a day for the same international destinations available from IAH.
The A-380's meant for slot restricted airports like Tokyo Narita and London Heathrow, not necessarily the New York to Dallas market. It makes sense on some routes (like Tokyo to London) but not on most. I wouldn't expect Dallas or Houston to rebuild for the A-380 unless American or Continental buy it. And I doubt they will. Memphis might, if FedEx actually takes delivery of them.
As you said, the recent U.S. trend has been for increased frequency with smaller planes and increased flights to European non-hub airports. Most American carriers don't even fly the 747 any more, opting to fly 767, 777s and A-330s overseas. Continental has even begun flying 757s to some secondary European airports from Newark.
The 787 and 747 kickers address the dispersed American model, whereas the 380 addresses the concentrated Asian model.