Yes, I've seen them too. But it's one thing to force bees in a box, and another for them to choose it. There needs to be some tests, like robo's on the box size, showing no difference between a fixed box and a swinging box.
Provided one has trees, I think it would be very easy to rig a pulley system, raise the box up, catch the bees, lower it and transfer the frames and raise it back up. A lot easier than figuring out how to lower it down while standing 10-15 feet on a ladder.
I had on figuring something out with pulleys even if I fastened it to a tree. Then I thought, why not leave it on the pulley and not have to worry about climbing a ladder when I caught the bees. You could make it self leveling and be able to gently lower it without banging them around in the box as I would imagine climbing down a 10 foot ladder struggling to hang on to a box. Or accidentally dropping it! I tried to imagine tying a rope around it and lowering it from the top of the ladder, but could imagine all sorts of things to go wrong, besides trying to keep it mostly upright.