On hover it could display another tooltip which we can describe the serie.
I tried to do it but there're some fixes to do.
I'm going to allow fixed width legends in my application and let the end user choose between wrapping and ellipsis for legend item texts that are too long. In case of ellipsis, a legend item tool tip would be ideal for displaying the full text.
Søren Schrøder commented
Tooltip on legends would be nice indeed - I have a graph with 30+ series, which i legend by their symbol to avoid a massive legend-block. A tooltip "on mouse over" legend with long title would be awesome, especially for fixed width legends