The "goal" if for ATL to be a true Latin American gateway. JFK currently has more flights and most probably always will. This is because so many Latin American airlines fly there themselves. No single airline has developed JFK into a Latin American hub for them (AA perhaps, but nowhere near to the extent of MIA.)
Remember DL's extensive operations to Mexico from ATL in cooperation with Aeromexico - increasingly DL-operated.
By the end of this year, DL will have nonstop service to the following countries from ATL:
Mexico, Costa Rica, Panama, Guatemala, San Salvador, Venezuela, Colombia, Peru, Brazil and Chile.
That's not bad at all in my opinion considering they only started this build-up 2-3 yrs. ago.
DL also wants to start service to EZE, Argentina - that's the big fish and will be tough to get. Also, Montevideo via GRU; more routes to Brazil (from JFK to GRU and nonstops ATL to GIG); Quito and Guayaquil, Ecuador via BOG and La Paz, Bolivia via LIM.
These are not rumours, but came from the DL web-site - they had a map of their planned routes to Latin America. Can't find it on there anymore though.