I'd like to see separate cooling chambers that have removable doors to access different sections... CPU, GPU, PSU. Much like the Antec P180 case, but when you removed the side panel you could also remove the appropiate side door for each section.
A back plane for the HDDs would be swell.
I'd also like to see the Cosmos in all black.
In fact, a hybrid-clone of the HP Blackbird 002 case would be great, though the "foot" isn't required (I like the Cosmo's "handles" better) nor is the slot loading drive bays either.
I do love the tool-less design for the optical drives. Love the HDD config, but don't really get the cooling thing for the HDDs.
Also, I really like the idea of the coverable I/O port up top. Maybe perhaps make the case a tad bit wider to allow better cable management behind the mobo. (I don't have a Cosmos, waiting for a Blackbird clone, which is why I'm making these suggestions.)
But, if I at least see the covered I/O port, and seperate heat "chambers" like the P180/Blackbird, then I'll buy a Cosmos. While a backplane is awesome, it's not required as long as cable management is workable.