I had 1.6.9 on the eMMC module and saw the news for the 2.1.1 update, so I figured I’d update it on the XU4. Big mistake! Won’t boot anymore, tried rebooting it by unplugging it (yes, I read the news piece LOL), and still nothing. Next time, warn me before you go and remove eMMC boot ability from the update will ya? 
Now I gotta roll the damn thing back! grumbles Glad I kept the games on the USB thumb drive!