The initial release of sankey diagrams includes link.label which can be used to include extra text for each link that's only displayed on hover. Currently though, nodes have no such capability - their labels are displayed on the diagram and there is no way to display more or different information on hover.

While we're at it we should extend custom styling to sankey hover.

See https://github.com/plotly/plotly.js/pull/1582/files/8d021e0640a44da68a333426d77035ff67e27108..4d3ce9203fc6c2a0ffa21d9236708655b689e636#r115788926 for more info