Unfortunately it's not the MC doing the spanking *yet* (and I doubt that will happen before 0.8+). Other than that, I find myself in complete agreement.
Edit: Come to think of it, there's already precedent for two people conspiring to spank the 3rd (Emily's Revenge). Amy is hardly a stranger to intrigue, so there's plenty of potential for plotting... and spanking behind Rachel's back even before the MC takes over those duties officially.
MC could try to use Rachel as a threat in the background to avoid, similar to Sister Rivalry or Cat Fight or Rachel's Path.
Spank a bad girl so the other girl won't tell Rachel. And then switch the girls. Requires some diplomatic talking.
Since Rachel won't spank Amy, mc could argue that if he doesn't spank Amy, Emily would tell Rachel with consequences for both mc and Amy, similar to the Amy sacrifice event with Susan. On the other side Amy won't tell Rachel about bad Emily if Emily is spanked by mc. Requires that mc's spankings are preferable to Rachel's punishments.
Sister Rivalry is special since it includes Chloe and she probably would have tried the strap anyway if mc would have suggested it, but probably not in public and not with Emily watching. Still Chloe was happy when Emily was caught peeping, got a few slaps and did some playacting. So Sister Rivalry was another step forward for Chloe as we have seen on the island.
If there is a spanking by mc in sight, Chloe is like a kamikaze, willing to throw herself into it and drag along the other girls without hesitation.
Edit :
Chloe would probably watch when mc spanks Amy and Emily and would make comments. So after the spanking when Amy and Emily have a short corner time, Chloe might go a comment too far and mc could allow Amy and Emily to give Chloe a revenge spanking where she goes over Emily's and Amy's lap by order of mc. (Similar to Cat Fight where Amy spanks Chloe.)
It is easier to host such an event on the island than on the yacht. However at 8pm during workday when Rachel is busy with Susan, Amy and Emily are usually in Emily's room and they are already arguing close to a fight, they just have to go one step forward and mc has to step in. So this might be a good time, although the location is close to Rachel's room.
Meeting at a later time like 2am (similar to Truth or Dare or Games & Alcohol) would be more unpredictable due to Emily likely drinking alcohol.
