fwiw even the tiny "drag a ball through a bunch of rotating bent blocks" lags quite noticeably when I start dragging. so I suspect it struggles even when the space is fairly small.

neat technique though!

I suspect this might almost never be a problem. Because say there are n things on the canvas and they have occupied n slots, you lift one of them and want to drop it somewhere, there are only n spots to drop it to. This gives only n next states, even though there are n! permuatations. You have to drag and drop again to reach some other state.

I didn't read the paper yet, but do you they do space partitioning based on events direction ?