If there is a configuration nobody would use, and if that configuration could be dangerous, I would opt for a removal of that configuration. Single channel approach is of course fine. But could anyone please tell me of what use the auto-retard is in that configuration? Being to lazy to pull the levers to idle is not an argument (IMHO).
Very well put.
No additional warning/checking system required. Simply disconnect the unneeded A/T retard function for other than autoland approaches. Problem solved.