Some thoughts. At some point, given the fatalities and the world becoming more litigious not less, this is going to be in a civil court. Be that the pilot, operator, organiser or regulator, depending upon the cause and underlying factors.
Of course we assume that there is only one investigation when clearly there will be investigation by the insurer and the state. Neither of whom need to be interested in ICAO Annex 13.
The AAIB report is of great importance because for many victims it maybe the only thing that gives them some visibility as to what has happened. One thing to remember with Rogers v Hoyle is that ultimately the prosecutions case collapsed. In fact arguably the biggest issue for the use of AAIB reports in court is that, due to the nature of our system where one party wins the other looses, the very credibility of the AAIB gets challenged.
Therefore its the AAIB that have much to loose and whilst you might not think a state accident investigator has a need for
PR what happens to them if (for example) opinion is drawn from other sources? After all if you take the German Wings Airbus that crashed in the Alps it was not the BEA that released the cockpit being locked information.
For the AAIB the biggest challenge I see is communication that suits 2015 and all the desire for information. Does that mean binning reports on some accidents? After all where someone flies their PA28 into a hill in fog or running out of fuel, forgot to use carb heat with the pilot only being lost - does chapter and verse on this really do anything to promote flight safety??
Balanced of course with some quite serious events taking circa 2 years to report on - Glasgow for example.