A and C:
While not being in a position to say exactly why Boeing have decided on this plug repair it seems like it has not been driven by conventional composite repair techniques but it has rather more in common with metal repair techniques.
Been pondering over this during the day and one thing I realised... MAYBE it is because the damage is so close to the tail fin. This would MAYBE make the scarf joint unreliable (because there would be less material for the angle on one side) regardless of pegs, nibs and hooks, and thus they opted for this intriguing solution. Very interesting indeed.