If you've been waiting for Nougat to miraculously appear on your SHIELD Tablet... keep waiting. This is not the update you're looking for, but it's an update nonetheless. There will be minor improvements to both SHIELD Tablets including, but not limited to, an updated Vulkan API and security patches.
The changelog is identical for the SHIELD Tablet and Tablet K1, and here it is.
- Conformity with Vulkan™ 184.108.40.206 CTS
- Fixed boot loop issue with certain SD cards nearing their capacity limit
- Fixed Android Privilege Escalation Exploit (CVE-2016-5195)
- Overall stability and security improvements
On the Tablet K1 this is update 1.5. On the older SHIELD Tablet, this is update 4.4. Both are still based on Android 6.0.1 Marshmallow. Sure, we would all like Nougat, but at least Nvidia is keeping up with updates to the original SHIELD Tablet. The updates are starting their rollout today. Give it some time if they aren't showing up quite yet.