Most of Cobb County is gross; it's where you live if you are scared of cities and black people, but still want to trick people and tell them you live in Atlanta. Historically, it's where the Cherokee Nation was until we Trail of Tears'd them, so it's got that going for it. But this location is right on the perimeter, so it's not really all that far "outside" the city.
Part of the T-SPLOST that got voted down, if I recall correctly, was a rail line up I-75 right to this location. Even though that didn't pass, I would imagine that idea is still kicking around. And having the stadium there might kickstart that project back to life.
Taxpayers will surely be footing a good bit, and they will also surely be told that it will pay for itself in benefits, which will surely be false. Why don't we go see how much money Gwinnett made on their stadium...
There is plenty of parking at Turner Field. It just goes on and on... however trying to drive out of the area after the game can be hellacious. And MARTA and Turner Field have had problems from the get go; the best option has often been to get off the train and walk for a mile or two.
That said, I can't imagine how the proposed location will be any better for traffic/parking. Yeah, it's near a major junction, but so is Turner. It's even farther from any extant MARTA line, and the surrounding surface streets can't really handle that load, as currently constructed.