Update worked on the 3rd attempt, boys! No brick tonight.
It's frozen. Reboot it. Same happened mine last update.
It may brick ..but it's clearly frozen so the only choice you have at present is to pull the power .
Mine did that too. I unplugged it and when it restarted it had a notification that the update failed. So I tried again and the second time it rebooted and seemed to freeze as the box didn't even start booting. Unplugged again(two dances with death!) and it booted back to the homepage, and then the third time updated fine. I think it's tough to brick these.
Mine got stuck exactly like that after the last update, just reboot it (I know it's crazy scary, but mine finished the update easily after I plugged the power and connected it back).