Martin offers a carbon fiber case; it costs a hair under $3K. If you could do it for $400, I imagine you could sell them.
As to the shape, flight/road cases aren't designed for carrying, they're designed for shipping; having spent way too much of my life loading and unloading trucks, I can assure you that rectangular is better - it can easily be fit into a load in a stable position, while guitar-shaped can't be, and thus is likely to move, and movement is where damage comes from.
Your idea about an end-opening case is interesting, and you make good points in favor, but it seems to me that sliding the istrument in lengthwise has some drawbacks:
you would, of neccesity, be inserting it head first, thus leading with the weakest part of the instrument;
it seems to me that a space loose enough to accept the instrument in this way would be looser than the traditional clamshell opening, thus allowing the dreaded movement;
the tuning machines & string ends sliding against the foam would soon destroy it.
If you can get it going, it would definitely be a worthwhile project - close to flightcase proctection with close to gigbag weight, at that price? What more could you ask?
Peter