> "The plan" look like a plan that needed to be actively managed by the uniquely special people involved - the same people, because they travel through time actively managing it - rather than an actual inevitable projection of history.
It was a rather important, though not initially revealed, point in the original trilogy that the plan was a plan that needed to be actively managed, by uniquely special people (including, but not exclusively, the strongest telepaths that could be found and gathered.)
Revealing this before the Mule is a radical change to the structure of the story, sure, moreso than changing the nature of the specialness of the guardians.
Right, the radical change is showing the Second Foundation getting built (and it having interesting reasons, in part due to individual mistakes, why it is getting built very slowly in time) not that the Second Foundation exists.
It's definitely an interesting storytelling change, and probably for the better. Second Foundation in the books is very much a seat of the pants deus ex machina where Asimov seemed to write himself into a clever puzzle with no easy answer and cleverly solved it "at the last minute" with a retcon, then sort of took another trilogy and a half to complete the retcon and deal with the consequences.
It was a rather important, though not initially revealed, point in the original trilogy that the plan was a plan that needed to be actively managed, by uniquely special people (including, but not exclusively, the strongest telepaths that could be found and gathered.)
Revealing this before the Mule is a radical change to the structure of the story, sure, moreso than changing the nature of the specialness of the guardians.