"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
More iPhone Nano Case Design Photos
For completeness sake, we should report that XSKN has now posted the entire series of iPhone Nano cases for sale. Again, we have our doubts about the release of an iPhone Nano, yet it's hard to deny that the two previous case designs that were posted on XSKN did accurately predict upcoming products.
As with previous product shots, the actual iPhone graphics shown within the case are simply existing iPhone promotional shots and do not necessarily represent what the iPhone Nano interface would look like.