I was thinking about this feature (highliting trace based on legend hover) and it is really nicely shown in the link attached in this original post so I decided to bump it. Before diving deep some hacky paths, does someone managed to implement this? I believe that there is no way to catch legend hover so the only way would be to implement legend as some another type of component. Another idea is to hack default legend click events so i.e. on double click all other traces do not diappear but get dimmed.
(now I noticed that this is Plotly post, maybe it would be more suitable for Dash)