If the lawyers succeed in the above scheme it will, perversely, be a kick in the teeth for all who want open and thorough investigation of air accidents (for all our disagreement, I place the OP in this category). The vast majority of safety incidents are self-reported and this will halt at a stroke if CVR evidence is grabbed for the purpose of criminal prosecution; particularly in cases such as the Super Puma where there is no suggestion by anyone of a crime having been committed.
The redaction of the Glen Ogle transcript provoked discussion. AAIB policy is that such transcripts are NOT published unless it contains evidence that bears on the cause of the accident. May I suggest the Glen Ogle redaction was merely following the same protocol rather than evidence of something to be hidden? Perhaps someone familiar with BOI procedure could confirm.
Footnote: the pilot who led the original pilots' union campaign for introduction of CVR's was the father of one of the MOK Chinook pilots. what a twist of fate that he should see his own son posthumously blamed for an accident with no CVR two decades later!