Tranquil PC has released a first fanless 3rd party case for the Broadwell i3 and i5 NUC. The Abel M2 case is sold in two different versions, with and without a RS232 serial port.
They are offering the case together with the Maple Creek based enterprise versions of the Broadwell NUC motherboard instead of the more consumer oriented Rock Canyon. At the moment the case is not sold separately without the motherboard. The i3 version with the motherboard will set you back £328 and the i5 model can be had for £450 (both prices excluding VAT).