The two great fits DT for a food hall are the greyhound station (which obviously won't happen) and the landing. Go in and do some renovation to make the layout smaller and more open to the streetscape / water and you have a great centrally located food hall.
When I travel to different cities I always try and look up the local food scene, food halls have made this easy and people travel just to visit them. Some of the Food Halls I have visited are: LA the original farmers market & Grand Central Market DT, Boston Faneuil Hall (even they are building a new massive hall for 2019), Tampa of course with Armature, DC Union Market, NYC has several and the other one I have visited is Anaheims Packing District.
These spaces allow not only for local artisans to set up shop and be creative but it also allows for a place to gather. It is a destination for many people and in this millennial age it could thrive in Jax.