Regarding the questions:
1) It will be possible at some point when we add the onLegengLeave event as this will allow us to dynamically add the styles only when over the legend element.
2) The custom visual is a custom drawn SVG element that the developer has to draw instead of the built-in item. This means that everything including the position, length, etc has to be custom drawn, this is how the drawing API functions. In this case, we can suggest a method that will calculate the correct position based on the font size. Still, I agree that this can be a lot of custom modifications to only change the shape of the legend item. If you wish we can log a feature request to allow changing the shape to a predefined number of shapes.
3) HammerJS is required for the Chart events, but the reason why we do not have it in the demos comes from a limitation we have using stackblitz for many demos. We have to send a fixed list for all dependencies that will be added for all demos. As the hammerjs is needed only for the Chart we do not add it in the default list to not load it in all non-chart demos. I hope I was able to describe this correctly.
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