I updated to all the latest wireless drivers (Proset 17.0 Bluetooth 3.1) and tried Bluetooth again. I successfully paired my BT mouse and keyboard. The mouse took 2 tries. The first try the NUC thought it was successful, but the mouse continued to blink its find me signal. The second try worked and the blink shut off. Both devices worked successfully for a few days.
After I upgraded to an SSD, neither device worked. I tried to delete and re-pair the mouse and it always behaved like the NUC thought it was configured, but the mouse kept blinking.
It seems unlikely that the SSD by itself could cause this problem. Of course I did power off the NUC (for the first time since BT worked) and we all know that has a profound effect on a DN2820. It also seems reasonable that there is a timing related problem in the BT driver. The faster SSD could make it fail always while the slower HD made the timing close.
I should note that I am on the latest BIOS. I hope this report will help your BT Driver team figure out whats going on.
Another note: The newest drivers seem to have solver the WiFi performance problem I had seen previously. My cable tuner now can successfully stream live TV to my NUC without breaking up.