A bit of debate going on on YouTube about BHX being able to handle the A380. Someone has mentioned that the A388 has very good take off performance and could take off with a full load from BHX safely as it would not require full tanks of fuel to reach DXB, and that it performs very well on runways significantly shorter than BHX's.
Reading some old topics on Airliners.net, Turkmenistan were to start YYZ from BHX but this didn't go ahead. Uzbekistan operated a service to JFK for a period of time; for a while in 2001 and then was resumed in 2003, then terminated altogether.
Would Delta work at all at BHX? Of course I think it'd be down to the 'start-up package' and the aircraft used - I think if they flew from JFK, more people would use it, more so than Edinburgh.