Does this help, or are you looking for more than 2U?
http://www.intel.com/content/www/us/en/support/boards-and-kits/000006238.html A1U44X25NVMEDK and A2U44X25NVMEDK BackPlane Kits for Server Boards...
http://ark.intel.com/products/81802/2U-Hot-swap-Drive-Cage-Upgrade-Kit-with-4x-NVMe-SSD-Support-A2U44X25NVMEDK# @specifications 2U Hot-swap Drive Cage Upgrade Kit with 4x NVMe SSD Support A2U44X25NVMEDK Specifications
The kit is meant to be used with Intel supported chassis, if you want to give it a try with a third party chassis we suggest you check with the chassis manufacturer for compatibility.
You will find a picture on how it looks in our chassis in the following link on page 57: