To Prada, #682:
A failure of the pressure bulkhead is a logical explanation for the separation of the rudder and horizontal stabilizers and a picture of its condition would give a clear answer.
Bulkhead failure as a reason for a loss of rudder and stabilizers can be found with the BEA Vanguard accident and also the Japan Airlines B747SR ditto. In the latter case, the rudder and a big part of the vertical stabilizer separated from the aircraft and those damages is actually quite similar to those pictured on the MetroJet A321 wreck. It is evident that the vertical stabilizer is not only missing the rudder but also an "L shaped" piece including the top while only the forward piece of structure (which folded backwards on impact) remains.
Another possibility is a separate failure of the horizontal stabilizers.
Based on the wreckage, it is evident that the rudder and horizontal stabilizers separated from the aircraft and landed in a different location, which is the reason why the rear pressure bulkhead will be suspected until more data is available. If it turns out that it is completely intact, then there is another cause for the separation of the rudder and stabilizers. Delamination and failure of the vertical stabilizer could be another possibility and it could very well have hit the horizontal stabilizer (this happened with the Boeing 707 over Mount Fuji even if it was caused by severe turbulence).
My take on existing evidence is a failure of the tail surfaces of the aircraft caused by either a failure of the pressure bulkhead, failure of the vertical stabilizer due to delamination or something happening to the horizontal stabilizers.
It is necessary to document the condition of the RPB, rudder and remaining structure from the vertical stabilizer and also the horizontal stabilizers including the jack screw. The flight recorders paired with QAR (if the latter survived) will give more answers, especially if there is recorded data for the same amount of time as the FR24 provided (approximately 25 seconds after the initial event).