Through the answers given to both this and that question, I managed to create something that feels a lot like instanced lines. The positions are made right through an offset attribute (using a THREE.InstancedBufferAttribute).
However, I don’t get how to deal with scaling and rotation. In my use case, I have instanced meshes that populate my scene, and I would like to have instanced lines at the exact same position/rotation/scale as my instanced lines to give something like a wireframe effect.
Many thanks for your quick answer (and for your previous answers to the questions I linked). This looks like exactly what I need! I will need a few hours to understand how it all works and whether it can fit my purpose. More soon!
It does solve my problem perfectly well. I was looking at mesh level instead of looking a geometry level. You codepen was very helpful, many thanks for taking the time to put it together in such a clear way.