You would think it would be a risk legal people wouldn't be willing to take.
Where would the management of AsA lie if a midair was to occur whilst the rated person was on the toilet and a non rated person was in the chair?
What also happens if the only rated person on duty has a family emergency or medical problem that needs for them to go home immediately, who would fill the chair then ?
I can guarantee one thing, rather than be dealing with the issues in that memo the people that issued it are probably attempting to hunt down whoever posted it on here too!