According to the AJC, MARTA has officially cut the Braves shuttle, starting next year. While this will affect some attendance at games, it likely won't affect attendance to the point where the Braves organization will do anything about it. For a detailed overview of the limited alternative options, go here for a story I wrote exactly a month ago to the day.
It's a shame this got cut, for the people who rely on it, but it was likely the right move by MARTA.
While I don't recommend it in the middle of the summer, in the spring and fall the walk from either the Georgia State station or Five Points is just 15 to 20 minutes to the stadium. Perhaps the City of Atlanta and MARTA and the Braves will do a "get in shape with the Braves" campaign next year to promote physical fitness. Heck, they could even block off a lane and have drink stations setup along the way to and from the stadium.