Additional FDR data gathering?
Could the FDR include a channel (or better two) for cabin pressure, with very high resolution? If two, one at each end. If there were to be an explosion aboard, there would be a sudden cabin pressure rise, then presumably, reduction in pressure. If two sensors, the timing and differential would give you an idea of the fore/aft cabin location.
It won't help here, but could help in a future crash to rule in or out, a cabin explosion...
To carry the idea to the next step, what if a cabin pressure change exceeding a certain "normal" rate, triggered a 7700 squawk - no pilot action required. ATC knows that a dramatic cabin pressure event has occurred - even if a battery powered self contained transponder is falling free, and sending mode C on the way down.