This is actually something you can do with Tabletop Simulator on steam, as I'm using it for that exact purpose. It even uses JSON as the underlying data structure. Granted, it's proprietary and not free.
My room mate tried to use that and he said it was garbage. The thing that I remember was having to type file paths manually, but there was a bunch of other specific and egregious problems he pointed out. Beyond that though, 3D brings nothing to the table; it's just a gimmick.
