That makes perfect sense to me.
I just experienced an issue when making a post to explain whispers to my staff through examples, but some mistakes in the example topic have resulted in “hidden replies” (deletes) and whispers in the same view that just make for confusion for new staff members. I wouldn’t blame them for thinking it’s not worth trying to understand the feature.
Is there any reason not to allow changing the whisper state within the ninja edit timeframe?