I've had the opportunity to investigate a military accident (dive into water @550 knots 50 degrees ND, and to see the wreckage first hand of a 250 knot fly into the water in (near) level flight. In addition, I had the opportunity to participate in almost the entire AF447 thread. QZ8501 was not a dive into the water. A high speed dive would shatter the aircraft into its component bits & pieces with the leading component pieces more highly fractured than the trailing components (due to deceleration).
From the damage observed so far, the aircraft entered the water at very low forward speed in a near level, slightly left wing down attitude. The major velocity component was downward. By comparing the damage observed with AF447 and with some of the events of the Perpignan A320 accident, there is one glaring difference. The vertical stabilizer remained attached to the fuselage structure until the tail was crushed from beneath. Instead, the skin forward of the VS shows a small section of fore and aft force induced compressive wrinkling in addition to the vertical compressive force induced folding along the stringers lower down. Below that, the structure was shattered and is missing with damage extending further up the port side than the starboard side.
In other words, it hit the water slightly left wing down, with minimal horizontal velocity, in a flat attitude with relatively high vertical velocity. I'm open to differing opinions, but there is only one way I know of to put an aircraft into the water in this way, and that is a flat spin (as differentiated from a nose down spin).
Transport aircraft are not intentionally deeply stalled during flight testing nor are they spin tested let alone training pilots how to recover from a full stall or a spin. For this reason, if a spin is entered at altitude, it is likely to continue. Often flat spins in jets are not recoverable events and are dependent on the specific aircraft characteristics (mass distribution-types of control surfaces, general planform etc.)
I know some of you fly aerobatics including spins however, flat spins in larger aircraft have an additional hazard in that the crew is located far from the center of rotation, and thus even a modest rate of rotation in a spin creates disabling eyeballs out g effects. For example, in the F-14 front seat, you had to lock your shoulder harness at the beginning of the event or you would be folded over in your seat and unable to eject. I don't think A320 pilots would be particularly effective in recovering from a spin if they found themselves involuntarily staring at their kneecaps
.
Assuming that the foregoing analysis is in the ball park, it will be very interesting to learn how this departure from controlled flight developed.