It is a clever idea, but needs some UX love. Drag/drop to move around, but I have to click to open a dialog to mark it as done... There should be a way to drag it to a 'done' bucket. The list is broken into the four quadrants, but I cannot drag/drop in the list to set a specific priority, which would be critical when a tasks is dependent on another. In general, algorithmically prioritizing the list based on position within a quadrant is questionable - matrices like this communicate broader strokes of prioritization, not a opinionated list order.

Still, the idea has merit. It just needs some work to move forward.