@rudderrudderrat
Read the 3rd interim report. This was a very specific procedure within AF for a long-haul flight whereby the crew consists of a Captain, F/O and a relief pilot who is not a Captain. The Captain is supposed to brief the rest of the crew as to roles and responsibilities (including parameters for taking control) prior to the flight or at handover. The record suggests that this was not done.
I honestly don't think you're going to find any technical reason for this - handedness is not an issue, and as it seems relief pilots can sit in either seat it's not like F/Os get no practice with it on that side. I know some people want it to be about the sidestick, autotrim and lack of feedback but the odds are stacking up against it.