I mentioned several years ago that the reference pane could benefit from some more robust features. I would love to see the reference image rotate at the same angle when you rotate the canvas. This should be toggle able so you can have it happen when you want. I'd also like the grid to appear in it when you have it on in the main image. Other helpful features would be to have the panel and the canvas symbiotically linked so they zoom and pan at the same time if desired.
I would also like to see the reference image and possibly swatches linked to the main files so they open up together.