I highly doubt that UPS & FedEx have changed their billions of dollars of logistics system for a couple days of deliveries. There are two kinds of iPads: Those with engraving and those without.
Yes, those with engraving will be shipped from China as they are ready, but will not be delivered until the 16th.
But those without engraving will be shipped overnight from the multiple staging locations across the country (US & Canada). These are already stocked and ready to go. Tracking info has already been sent out. I have mine already. The only thing they are doing different from their day-to-day operations is to not deliver before the 16th, so the product is held at these locations until they are ready for transport (Thursday) to the local distribution facilities, then put on the trucks for final delivery (Friday).
And UPS trucks have been hijacked before. I personally know of one which was hijacked when leaving our manufacturing facility on S. Florida a few years back. But remember, hijacking a truck out for deliver with 4 or 5 iPads on it is not worth the risk. You would want the truck leaving a manufacturer with dozens or hundreds, not the trucks out for delivery.