CCDOT is currently working on a wide sidewalk along Floyd Road south of the Silver Comet Depot, a needed piece of this trail, and yesterday the Connect The Comet leaders presented their 4000-signature petition to Governor Nathan Deal's office to try and get things moving with the state and CSX.
The concept of connecting the SCT and Beltline enjoys almost universal support as an obvious great idea and excellent investment. The "process" apparently requires an official proposal to be submitted to the CSX Rails-to-Trails program, I assume this step can be done by GA DOT with limited or no insight into eventual financing if there's enough political pressure/will. The key is to get CSX and GA DOT negotiating a deal, PATH is certain to become involved for their generous $$ support and leadership as they were for the Silver Comet Trail. It won't be Cobb and/or Fulton/Atlanta since the right-of-way is about 50% on each side of the Chattahoochee River/moat.
The CSX tracks are completely paved over at Plant Atkinson Road, so the right-of-way in Cobb north of there is clearly unused. I understand that the tracks have actually been removed in places south of there. The most valuable piece is the rusty old trestle spanning the Chattahoochee River. Unfortunately, the right-of-way runs right through the infamous Atlanta water treatment plant (and next to the Cobb water treatment plant). Trail users might have to practice holding their breath for long periods ...