Technical overview

To support scrolling while dragging a card, our drag and drop library must be changed. At the moment of writing, it is based on the drag and drop API. It should instead rely on mouse/touch events or pointer events (the latter does not support IE11).
Drag and drop API suppresses all mouse / keyboard events once a drag has started. We don't want to reimplement ourselves the browser scroll behaviour, which means we must not base the drag and drop library on this API and use the lower-level mouse or pointer events.
Moving to mouse events means writing more code and handling the "drag mirror image" (the image that follows the pointer) manually. It means detecting ourselves when the pointer enters / leaves a potential drop container.

As as side-effect, we will be able to support programmatic cancel() and support cancelling drag when the ESC key is pressed. That was not possible with the Drag and drop API, because there appears to be no way to cancel it programmatically.