I had similar thoughts and wonder if it will be deemed safe. A simpler design might be a fixed tube with the stairs in going up to about an inch or so below the surface with a clear cover. Then you could yank it open if things failed or in normal use some outer tube could rise a couple of inches to stop water falling in and the inch of water be drained.
It wouldn't surprise me if there were some sort of backup system that could be deployed manually. The video also suggested they could drain water into the floor below from where it would flow through pipes to ground level. The video suggested that there will also be a "lifeguard" stationed in the pool.
In any case, this is more about having a show-off design than something people will use other than as a one-off to say that they did it.
