We are doing a graph diagram using force directed layout, and are displaying various overlays of paths through the graph based on input data parameters. As I mentioned, this is currently all fine in SVG, however, we'd like to in the future be able to make those overlays a bit more dynamic in the graphic sense - by adding some effects that canvas makes easy. Also, our future drawing of the graph will include enough custom shapes and images/sprites that the canvas context + drawing objects will result in cleaner code than the equivalent SVG operations.

Also, and this part is a personal bias, I just dislike SVG and it's DOM for runtime graphics manipulation, and prefer the canvas API for it.