The Sankey visualization (currently 3.0.3) is surprisingly good, though still not quite ready for production use. The "Help and Support" link sent me to the PowerBI Community site, so I'll try to connect here.
The great strength of the current visualization is that it automatically maps single level data (source / data/ value) and is NOT a "category breakdown" subset of Sankey functionality.
Great! But... There needs to be more legends of amounts and percentages that can be seen without flyover, and I can't find, well, any at all! While I don't think I would enjoy getting into the main algorithm, I could conceivably contribute to improving the text items. If this is a developed-by-Microsoft item, then I'd like to submit requests to the team for enough features for the code to be useful (more than a toy). The only other option (ChartExpo) is in fact a category breakdown visualization, and none of my use cases would be compatible with a category breakdown Sankey. Bottom line: 1) is there an "owner" of Sankey that I can communicate with, or 2) is the Sankey visualization already open-source with contributions possible?