As someone who worked for Apple (and many other big corporations in retail) It seems to me that what would be likely is some sort of big change in the way they do training and how the store operates. I've been to tons of store meetings where nobody would tell you what it was about, and then they roll out the "gold standard service philosophy" or some such junk that they think will make the way the store works better.
I'd imagine lots of store meetings have had gigabytes of data that was locked down till the day before, so that doesn't seem to out of the ordinary.
The visual stuff being locked down just seems like it's back to school related. Typically visual displays came in the day they were being put up, but sometimes they'd be delayed by a day or so. I'd imagine it might be something a little more special than usual, but they probably just want all the visuals to be up the same day across the board.
EDIT: Also, the speculation on why there are only one back of house, or one genius, etc. That is probably only one store's setup. Often when we'd have these larger visual nights (pre Christmas usually) they were sprung on us quickly, so they needed to find anyone who could work the day, that usually meant people not working the next day (Sunday) and really anyone can do a visual overnight, and they're usually not doing anything related to their normal job.