The problem with Cuben is also the duribility. It is not something that I think would hold up to a lot of use. At least the way I use my gear, when I can use it.
How can they make sails out of it then? Millionare yacht racers aren't worried about what it costs, I would think they'd be concerned about it failing in the middle of a race. I don't know anything about it, maybe you are much more informed about it than I am. I have been eyeballing that MLD Cuben poncho though, it covers you and your pack and weighs about the same as a pack cover.