No, nothing to do with in-flight separation 'theories', but more to do with a heavy impact, surmised to be tail down. It is expecting a lot of a tailplane assembly in that situation not to cause tail section separation which leaves a light'ish structure to make its own way down to the sea bed, taking with it the FDR. No pinger any more - now find it?
As I say, I hope for all I am wrong. The sonar 'finding' so far has been brilliant. I hope it continues.