This issue covers the quantum/glass part of RT-14730. It's a common standard to provide a visual representation of the dragged data (an image floating with the cursor during DnD), not supporting it is almost a bug. We finally have an API for rendering nodes to images, so nothing should block us from providing this functionality any more.
I expect we will add the API to Dragboard, so it would be best if toolkit was either prepared to extract the Image from the Dragboard or accepted the Image as an argument of the startDrag call.