No planting, no foreshadowing, no hints, no explanation in the movies at any time.
So this theory is nothing but fanfiction. When a movie scene needs to be eyplained outside of the movie, thenit is the worst writing. It is very muh like explaining a joke.
No planting, no foreshadowing, no hints, no explanation in the movies at any time - all that only proves GL didn't set it up very well. It doesn't prove that GL wasn't trying to put it in there when he made ROTS.
In fact this kind of hasty construction of the storyline feels like standard procedure for the prequels. Nobody is trying argue that GL had it planned it that way 30 years ago.