Will the X1 update brick the system if unplugged while downloading/updating
Yes, yes it will. That's what happens when you cut the power to a system when it's in the middle of a firmware update.
Not while downloading of course but certainly while updating. In order for it not to the Xbone would require an internal battery back that is capable of maintaining the system for a few minutes after a power loss. Such a battery would be large, expensive and most definitely be inside of the system. --- The commercial says that Church isn't for perfect people, I guess that's why I'm an atheist.