You don't have to have a full cover.. Only the cameras would need to have a window of (sapphire)glass. The rest of the ski-mask could easily be plastic, as it's

You don't have to have a full cover.. Only the cameras would need to have a window of (sapphire)glass. The rest of the ski-mask could easily be plastic, as it's only used to display eyes. My guess is that it gives them a few cycles to improve the weight. The iPhone X was a monster in terms of weight