Suggestion:
It would be really neat if the legend could be movable by the end user.
My applicaiton will be plotting data and I can't predict which area of the graph will be clearest for legend placement. I don't want to hide important results, so allowing the user to move the legend to the most appropriate area would be really powerful. Perhaps snapping to one of the corners.

The work by @NicolasLairNET in PR #3650 that is nearing completion looks like it might be similar?