Oh that's a cool idea! It's definitely more natural than putting an intrusive UI indicator. Also, I'm not sure I see any way to softlock in level 6? Unless you somehow manage to put the box down next to the goal, but I'm not sure that's possible.
I went back to test it and you seem to be right.
I didn't realise that the box fell through the underside of the thin platforms, so I thought it was possible to get it stuck on one of those.
