Many Possibilities, One Cause
I just joined this forum after being sent to it by Bing a number of times so I could post. There seems to be a lot of confusion on here, particularly regarding stalls.
1. Bear in mind that the FAA and manufacturers of transport category airplanes publishes procedures for stall recovery at "the first indication", which can be the burble or stick shaker.
2. Sweptback wing airplanes can have vicious stall characteristic and are prohibited from being intentionally stalled at low altitudes because it takes so much altitude for recovery. For example, the Hawker HS 125 crew manual contained an admonishment against stalls below 10,000 feet. That didn't stop one crew in my area from decided to practice stalls at 4,000 feet while on a training flight. They're not here anymore.
3. Regarding the video, bear in mind that the vehicle and 747 are approaching each other at a high rate of speed. I've been around airfields all of my adult life. When observing an airplane coming straight toward you, it will appear to be in a nose up attitude. This is also true in flight. There is really no way to determine the deck angle of the airplane from the video.
4. There were thunderstorms in the vicinity of the airport at the time of the crash. The METARS have been posted on the Net. Thunderstorms may be accompanied by dry microbursts, which can ruin your day. There was a rash of them from 1970 to 1985, but it's been several years since an airline aircraft was lost to one in the US, at least. Vertical winds in a microburst have been recorded as high 168 MPH - straight down. Escape procedures call for as high of a nose angle as it takes to get the airplane climbing, and maintaining aircraft configuration.
5. Regarding a load shift. If it's going to occur, it will most likely be during the takeoff roll when aft Gs are most prominent (and they're not that much.) The Gs experienced at rotation are positive, not aft. The military and civilian cargo operators tie loads down for restraint in all directions, usually 3Gs forward, 1.5Gs lateral and aft and 2Gs vertical (in military transports, if passengers are in front of the load, the forward requirement is increased to 9Gs.) There is also a down requirement but its met by the floor. Apparently some vehicles have to be palletized to load on a 747-400 rather than driven in. In that case, the load is secured to the pallet, which is locked, then additional restraint is applied to the airplane floor. For a pallet to shift, the locks and the restraints would have to fail.
6. I once was a simulator instructor. The training industry and manufacturers has determined that it takes an average of 10 seconds for a crew to even recognize they have a problem, let alone start to deal with it. Until the transcript of the CVR is released, no one is going to know what the crew thought their problem was and what actions they took.
This is a terrible tragedy - all fatal accidents are. I'm sure something will eventually be published since it involved a US crew working for a US company flying a US registered airplane.