Hi @spuder, I worked in 3d-viewer development. I know nothing about the phyton scripts. From what I know from the 3d-viewer it is not possible to get the renders from any other place. It may be possible in future… What is your propose to get the renders by an external script? Would you like to share your wishes with us?
You can also fill a bug and mark it as a wish here: https://bugs.launchpad.net/kicad
I’m collaborating on an opensource keyboard on github. Before anyone contributes a change to the pcb layout, they are asked to run a script that generates plots (in pdf form). Those plot can then easily be compared to see exactly what changes were made.
Here is an example. Things marked in blue / red are the difference between the two board revisions.
We want to extend the scripts so that not only do they generate plots, but they also generate 3d renderings. This will make it easier to see every change that was made.