This is definitely a positive development, as transferring in GRU is a big timewaster, and GIG-ATL avoids the customs madhouse of AA's GIG-MIA service.

The paucity of nonstop service to GIG is an anomoly driven by the fact that premium yields on routes through GRU are amongst the highest in the world. My understanding is that AA's JFK-GRU is actually the highest yielding flight in their entire route network, with lots of demand in the front of the plane.

GIG, in contrast, is primarily a leisure destination, with much less demand for premium fares. GIG is a great destination though, and commands consistently high fares even in Y. I think that it is a great opportunity for an LCC to come in and offer nonstop service, and wouldn't be surprised to see that happen in the not too distant future.