The main improvement I can think of is that while creating charts, it gives you a certain format of how it could look. If you want to create something extra and go more vivid and creative with how the actual chart would look, it allows for that option but could be improved to be more artistic or aesthetically pleasing. This sort of format is missing, and I think it would be beneficial to the analytics team if it can be more interactive, with the capability of D3.js, and give us more control over how our actual dashboard would look to achieve a more aesthetic appearance. The strict format of how you can shape those charts and that extra nuance you need to keep in code to get the exact possible results are the reasons behind my rating. The rest of the features provided by Plotly are extremely good.
