In addition to #396155, I'd love the reference images tool to have a sort of "subgrid" painted over it, based on the main grid that is shown over the artboard (see https://www.artistsnetwork.com/wp-content/uploads/2016/06/drawing-grid-method-Lee-Hammond-061616.jpg as a reference of what I mean). This would be useful for us who are learning to draw by eye, or in general for users who need to draw from reference with some degree of accuracy.
Ah, yes, I actually needed that myself today.