A couple of things about the ATL base:

1. NK opening the base, per the union, was nothing more than an attempt to stem attrition to DL. It is not an operational necessity like FLL, LAS, etc...

2. From the looks of what I've seen, and I mean this in the nicest way possible, the typical ATL pax on a ULCC carrier is probably not making the jump to flying Jetblue. It is what it is, but I would not hesitate to jump ship to DL. It really shouldn't even be up for debate. DL is not leaving ATL unless all of society collapses, and even then they still might be there.