My money's on a driveshaft failure.
Front u-joint or yoke lets go, the driveshaft hits the ground and drags for a bit while the car bounces around. Then the driveshaft caught on something. The driveshaft crumples up and gets caught under up the car. The car keeps going, so the driveshaft flips the rear axle under, and either the hangers/shackles or u bolts shear. The shocks just get pulled apart.
If you look at the video, you can see what looks like the bottom tubes of the shocks still attached to the rear axle.
Kind of the perfect sequence of events, but I've heard of it happening before. Mythbusters even tested it, trying to get a car to "pole vault" on the driveshaft. They didn't quite get that to happen, but they jumped the back end of the car up a couple feet. Looked very similar to the beginning sequence of the video, although the rear axle on the mythbusters car staying in place. But watching their video I can see how it might not under the right circumstances. With the original hangers or u-bolts and some rust I can see how it might work.
Just like this one...
[ame="https://www.youtube.com/watch?v=k9DVlnX0jIc"]Mustang Pole Vault - YouTube[/ame]
