I also love the transparency and am surprised it hasn’t been used more. Granted, it would be very difficult to achieve with natural materials and also be durable. A flag should be able to withstand an ocean voyage exposed to the elements.

I think you pointed out very well why it hasn't been used more: lack of durability. It has to be some kind of plastic foil, and it has to be thin enough to fly in the wind the same way as a traditional flag does, so it will degrade very quickly when exposed to the elements.

So, nice idea, but completely impractical, which makes it a gimmick.