Apple actually released Build 17B1003 yesterday afternoon (PST), not today. It apparently does fix the file sharing issue as reported by other MacRumors contributors (it was not relevant to my environment).
It also doesn't honor the "update later" option. When the notification popped up a couple days ago, I didn't know what it was, so I clicked "update later." Maybe 10 seconds later, I get an "update installed successfully" message. (Can't really blame Apple; just shows how serious this mess was.)