Who says it was at stalling speed at 4000’?

Pitot blocked by wasp mud dauber happened to an Etihad A300 with only a 2 hours stop in BNE on November 21st 2013 (called Mayday).
But indeed it is far too early to make such conclusion for SJ182
I just hope they could recover pitots and inspect them.
A B737 from an operator based in Jakarta lost controlled some years ago (they recovered hopefully) in high altitude, due to incorrect airspeed indication and incorrect procedure applied (PF remaining on side of incorrect speed).
During investigation they found wasp nest in PF side's pitot.

Let's wait the end of the investigation ; I just hope they will consider this possibility ; there is very small awareness within all operators based in JKT as well as for the airport authorities when it comes to dangers caused by the wasps and corrective actions to be taken, especially during the rainy season.
BNE is typical example of what should be done by airport authorities, as preventive measures.

If it speared vertical into the water with 400ish kn then from most part of the plane, especial the front, only small shrapnel will be left over. The impact with water can be the boom, the fishermen heard, since at those speeds hitting water or concrete makes no difference.

Good that they located the recorders in shallow water, so we will find out what happened.

I have see wasps start building a nest in a pitot tube within 10 minutes of shutdown.

WatchTheSkies

I posted a link earlier to the data I was using (it may have been deleted), but I'll use yours for simplicity.

Your own analysis shows an average track angle rate of approximately +10°/s during the last 11 seconds of flight (from around 8000' until impact).

I agree with that. So I'll ask again - where do you get a "left turn" from ?

Unreliable airspeed would have happened at takeoff, not at 11000 ft. Nothing suggests any issues before they suddenly went straight down.

Exactly that is why it has such a large tail... There are also not that many flying around, especially at that age. So more chance of unnoticed fatique cracks.

It has the same tail as every other classic 737. -300, -400, -500.

Photos
 

https://cimg2.ibsrv.net/gimg/pprune....7054c7039.jpeg
https://cimg3.ibsrv.net/gimg/pprune....03d1e2fd3.jpeg
https://cimg4.ibsrv.net/gimg/pprune....b3d151320.jpeg
https://cimg5.ibsrv.net/gimg/pprune....f6cdd11e0.jpeg
https://cimg6.ibsrv.net/gimg/pprune....ac706554e.jpeg

WatchTheSkies

Drag does not increase exponentially as a function of velocity. Without turbulence the drag is linear in velocity (Stokes' law). At relatively large speed it is quadratic (Rayleigh).

DaveReidUK

I am assuming the aircraft was inverted from 8000' as that explains the lateral speed increase and the revers from the initial 20s of left turn. So when you are inverted. From the perspective in the cockpit you are turning left when the heading change was +10°

Euclideanplane

There are different types of drag. The drag in the case of reverser unlock or severe damage is parasite drag. Refer to
www.skybrary.aero/index.php/Drag

DaveReidUK

The first 20 sec of the data is the left turn. I assume the aircraft became inverted as it explains the lateral speed increase and heading direction changes. When the plane is inverted, it was still turning left relative to itself, right if you are viewing the upside down plane from the ground, producing the +10°/s increase in heading

Look to Silkair in '98 for similarities.

Icing in the climb?

Explosions?
 

Could have been engine surges from a sudden/rapid change in attitude resulting in airflow changes into the inlets...

WatchTheSkies

That is correct. Parasitic drag refers to an additional volume of air stuck to the body of the aircraft and causing additional drag, e.g. such as with a windmilling or structurally damaged engine. It causes more drag than usual, but the dependence on speed is not different, as it says when quoting the page which you referenced: "Parasitic drag increases with the square of the airspeed". That is quadratic, which is bad enough, but not exponential.

Possible, but not likely. SOP is probe heat ON after start. As others have said, low CB activity in the area they passed through. Icing at 10000 ft in a CB is possible, but otherwise you need to get higher than 10-11000 ft before you encounter icing in this area. Besides, unreliable airspeed does not lead to a straight down descent.
Something severe happened very fast with this flight. Even if you lose control you will try to do something to regain control. That would show up on the data, but they went down fast without much input to reverse the situation. It feels like a deliberate action or a situation it was not possible to get out of.

I tend to agree with your guess that the aircrafts initial departure from normal flight was a left bank past 90 degree with an increasing nose down (relative to the horizon) attitude.
We will soon get the answer when preliminary data from the flight data recorder are released.