I'd be part of the market. I have been using DonkeyBoxx panniers that I cut the lid off of. I had Joe Valesko at Z packs make two custom fit cuben roll top bags that fit into the panniers. The panniers are really light (not so much aerodynamic at all) and could be ridiculously light if the one piece of metal were titanium instead of steel (the top of the box has a piece of steel running around all four sides to keep the box "squared". I also had Joe modify his cuben rain jacket to make it a bike jacket. I based the mods requested on a Showers Pass design. Basically I ha him add length to the sleeves, and add a drop tail. I haven't weighed it yet but I'm assuming it is pretty much the lightest cycling rain jacket out there. I have been thinking that a cycling poncho (or "cape" I think they sometimes call them) out of cuben would be great. They look ridiculous but keep you, your bike, and a certain amount of gear (whatever is on your handlebars, downtube, top tube) dry.
I think currogated plastic is a great thing to look at using. Super cheap, sturdy as all hell, lightweight. The best part is that you can get the price down to the point where you really don't mind replacing it if it is stolen or trashed. You could probably do a great handlebar box with it and attach it with zip ties