Here is a tutorial: https://rerun.io/docs/howto/visualization/extend-ui#custom-v...
And here is the corresponding code example: https://github.com/rerun-io/rerun/tree/main/examples/rust/cu...
To write your own graph visualization, you can look into the implementation of our graph view: https://github.com/rerun-io/rerun/tree/main/crates/viewer/re...
In the future we want to provide more types of layouts, dataflow is high up on that list. May I ask what kind of data you want to visualize? Since you mentioned Sankeys, in your case does the structure of the Sankey change as well, or do you only expect the edges to grow/shrink over time?