The Sankey Diagram as it is today is an extremely useful visual for showing network, process, or system flow. However there are some serious limitations that, if fixed, would make this visual TOP NOTCH.
(Most important in this list) Conditional Color formatting for the nodes and links based on columns and/or measures
We could show the status of each link/node IN THE SANKEY??? Mind blown.
Make labels visible not by the node size, but by the distance from adjacent nodes.
It's frustrating to have 6 inches of white space on either side of a node, but the label won't display because the node is small.
Have a button to restore the default locations of the nodes if they're moved
(Extra credit) Have an option to re-position the nodes to have minimal overlapping links