Considering all the external drives you can purchase an hook up via HDMI, USB 3.0 an all that I don't really see a reason for any optical drives or hard drives. Points of focus I would have in mind when designing an innovative case would be...
+ Optimal Heat Dissipation
+ Durability & Light weight
+ Space for up to 4-way GPU's of any size
+ Form Factor Compatibility Mini-ATX up to XL ATX
+ Lower Manufacturing cost thus lowering MSRP
+ Aesthetic Customization options for the Consumer
Note - Keep in mind as time goes on more an more stuff is become purely digital. Even storage is making it's move in that direction with Skydrive, Dropbox, iCloud, etc... Mac even offers a standalone tower that is purely storage called icloud that you setup in your house. Pretty soon a case will only need to have the functioning parts (motherboard, ram, gpu, psu)
So if you are releasing cases that you want to stand the length of time ahead of us with all the new digital stuff becoming more of a standard I'd go back to the drawing board an take what I said into consideration. Innovation is what you need to move your parts ahead of the competition.