imho I think you need to look for novel solutions to problems that occur to a builder and look at how that fits in with ^^
For example anyone can copy a standard atx case layout but perhaps one with a novel cooling solution such a ducting would be good. Cables are always a massive issue so how about incorporating a cable tidy system in the design. What about a hinged side door which operates an internal light when opened as oposed to teh usual slide door.
Installing drives and optical drives is a real pain - i'd love to see a proper modular easy to use design for that. Perhaps a themed or topical case would be fun.
I reckon experimenting with a different atx layout could pay off.
Think about how this case would be manufactured in the real world. Ease of manufacture is a real issue as time = money. why not use allen key bolts instead of screws for the design (so a single tool is needed to build the entire case and install bits) hell sell it as a flat pack DIY case. One tool to build it plus instrucions. Ikea do this and they've made billions. (actuall thats a bloody good idea!) - no labour to build it and lower shipping costs. a holder on the inside of the case for the tool(s) you need to tinker.
http://fastener-express.com/browsepr...ed-Qty-25.html
http://cgi.ebay.co.uk/Pro-Bolt-Anodi...QQcmdZViewItem
fancy and a little expensive but thats a customisable feature.
Can it be transported easily for lan parties.