Unfortunately, dash-leaflet does not handle clustering of more than 13,000 points… In truth… it does… But it locks up the browser for over 60 seconds before showing the page. So unusable in any practical sense. It also appears to be dropping thousands of points. Sadness.
So yeah, if anyone can guide us on how to cluster with mapbox that would be lovely 
looked into making a custom-dash component for this but currently seems daunting.