Drag and drop issues between Epics in work breakdowns

I think it would be a killer feature for the Work Breakdown Structure gadget if it was possible to drag and drop an issue in one epic to another epic.

Bonus points if you can also drag and drop a subtask from one issue to another issue.

I have no idea how feasible this is. I haven't seen any gadgets that provide this kind of interactivity so it's likely not easy or impossible but it would sure be great if it is possible.