I've updated the NUC to Sierra using the App Store successfully following the advice in this post
Direct Update to macOS Sierra using Clover
Read it first.
You need to make sure that you update Clover Configurator to the latest version first. Run Clover Configurator. On the menu (top left) hit update Clover... Then run Clover and Mount the EFI (bottom left). After you've mounted EFI then select the Update option in the bottom left of the Clover Configurator window. This will update the boot loader of your machine. After the update completes, save, then reboot.
After rebooting, enable viewing of all hidden files in Finder.
- Open Terminal (Finder > Applications > Utilities>Terminal)
- In Terminal, paste the following: defaults write com.apple.finder AppleShowAllFiles YES
- killall Finder
Then mount the your EFI partition using Clover Configurator. If you have problems mounting the EFI download
EFI Mounter v3
When you have the EFI mounted..In Finder, open INSERT NAME OF YOUR MAIN DRIVE\Library\Extensions -- a folder that was hidden before -- copy and paste *all* the kexts in this folder into the EFI\Clover\Kexts\Other directory.
Reboot, then run the Sierra update from the App Store. Performing these steps successfully installed 10.12 on my DC3217BY.
For some reason, on first boot I had no sound, but a further reboot fixed this (No idea why?).
I've had some issues with the wireless keyboard and trackpad not waking the mac from sleep and then not being able to be connected at all following a restart. It may be a USB related issue. I say may be a USB issue as I have had the same intermittent issues with 10.11. If anyone could shed any light on this I'd be grateful for any help.
Good luck