There is no way in either Qt Quick 3D or Qt 3D Studio to take advantage of instanced rendering where available currently.  Many high level 3D engines do provide support for so called Multi-Mesh rendering, being that you can instantate the same mesh multiple times in a scene with a set of differences between them, and that translate into one draw call (improving performance).

This could be useful for populating a terrain with trees, shrubs, and grass performantly without generated a draw call for each instance. 

It could also be useful for generating buildings based on vector map data for a navigation view.

This task involves researching what such an API would look like, and generating the necessary plumbing in the renderer to take use of it.