Working where I do, I sit at a desk pretty much all day and get interesting emails occasionally. A little while back I received an email that had a link to another persons blog where he posted a project he did for a class.
The Coke Bottle Project had a design for a newer squared 20oz bottle. It promotes a slimmer cap much like the coke bottles have now. Its square, so it has a much smaller footprint, making transportation of the bottles more efficient. A collapsable design more like some of the water bottles you get now days that once collapsed are more easily recycled. The bottle is also suppose to be 100% plant based being made out of sugar cane byproducts. Because its square it also has a cavity at the bottom for stackability, but speaking from experience I don't see them being stacked to high. Plastic bottles tends to lose stability fast when stacked higher then a certain height without being crated.
Overall I thought it was a really good idea and think it would work, but I much rather think that a new-age company or even a company like Pepsi would pick up the design before coke did, because Coke seems very traditional. Pepsi probably won't either though, because it would still cause for a lot of redesigning of vending machines, so maybe a new-age company will pick it up and then maybe Coke and Pepsi will at the same time shortly after.