If anyone is interested, I've developed an interactive visualisation plugin that enables exploration, analysis and visualisation of data in Totara Report Builder reports.
It uses the PivotTable.js interactive Pivot Table library and the plotly.js charting library to turn a Totara Report Builder report into a summary table with a 2-d drag'n'drop UI for manipulating this summary table, effectively turning it into a pivot table, which can then be rendered in a variety of charts.
The plugin is available for download at https://github.com/logicexpertise/totara-local_rbvis/releases
Note, only Totara version 10.0 is currently supported, however I intend to release versions supporting T11 and T12 soon.