Graphviz has a image width/height limit of 32768px for PNG images. SVG images do not have that limit, but I can't remember if I ever tried to export datsville as an SVG.
The snap metas work similar to the LDraw type 1 lines (subfile references). You will need the full subfile reference logic in your parser if you want to use the snap metas. I don't think that using the 3D mesh of the parts to determine which parts are connected to each other is easier than using the snap metas. There will be precision issues and if a connection isn't recognized you would either have to alter the 3D shape of the part or store additional connectivity information (which the snap metas already do)
The snap metas work similar to the LDraw type 1 lines (subfile references). You will need the full subfile reference logic in your parser if you want to use the snap metas. I don't think that using the 3D mesh of the parts to determine which parts are connected to each other is easier than using the snap metas. There will be precision issues and if a connection isn't recognized you would either have to alter the 3D shape of the part or store additional connectivity information (which the snap metas already do)