Cases are for gigging and the protection while doing so.Any external material shuold be strong and wear resistant,shouldnt hold moisture(or let any in for that matter),but still should be some what appealing to the eye...I like diamond plate.Interior material must be 'fine finish friendly',resist moisture and be attractive...I dont know much about fabrics so I have no idea on an exact material.
If the case came with free strings,picks e.c.t.then that would be fine.
The shape of the case is limited by efficiancy.You can go all out with exterior design graphics and slight shape alterations(like the coffin case)or even make a cyclinder like shape,but if it cant fit in a compact car its no use to a working musician.
Few cases are truly universal...ive yet to see a case that can hold a jackson v,bc rich warlock,gibson lp and regular strat with equal effectivness.If you can make true universal case,then that would be something.It would be worth the slightly larger size.
Compartments are a great thing too.I see no reason why you wouldnt be able to throw in a couple of your favorite fx pedals.
there should also be a tremelo bar cavity so you dont have to remove it from trem/locked trem guitars for transport.
I would imagine there would be multiple cavities to accept different tremolo positions...the cavities might look like a pinwheel.If its going to be truly universal,then it must accomodate left handed guitars as well as right handed.
It shold also sport rubber casters for smooth transport.
And above all...keep the wieght to a minimum!
Later! \m/
Try once,fail twice...