While ATL is a major metro area and is the "capital of the South", it just doesn't have the O/D to support a lot of routes that Delta doesn't already fly. DL uses ATL mostly for connection/transfer passengers, and DL would have tried the routes already. There is a reason why DL's brief expansion into China from ATL did not work, and why ATL-BOM (oft requested) has not launched. As hard as DL tries to make ATL have a flight to as many places in the world, it just does not make economic sense, especially when they have JV/alliances around the world, excellent transit hubs in Europe and Asia, and are building out international gateways on the U.S. coasts (first JFK, now SEA -- and a touch in LAX).

Lastly, DL doesn't have the aircraft in its fleet to expand that much more. Their aircraft are most efficiently used on long haul flights between hubs, between major business centers, and to captive markets (e.g. ATL-JNB/DXB). If/when DL starts getting deliveries of next generation widebodies, then the conversation can be revisited. But for now, Delta's most economical widebody is the A330, which a) doesn't have the legs for much longer routes that might be desired from ATL because ATL is so far South, and b) their 777 fleet which could reach most of those destinations being considered is being used on routes that waste their range (e.g. MSP-NRT).

As for ATL-HKG, it isn't happening, and won't any time soon. DL could not make DTW-HKG work, and ATL does not have the O/D to support it. The ATL-DTW-HKG connection was a mere 50 miles longer than a nonstop and that still didn't work for DL.