interesting tidbit.
One of Heinlein's comments on the rise of Nehemiah Scudder, from the same post script.
"The first of these unwritten stories, 'The Sound Of His Wings', starts shortly before 'Logic Of Empire' and continues for several years beyonf the ending of 'Logic'; it would have recounted the early life, rise as a television evangelist, and subsequent political career of the Reverend Nehemiah Scudder, the "First Prophet," President of the United States, and destroyer of its Constitution, founder of the Theocracy."
Elsewhere in the series, he explains why this story will remain unwritten (but it's evidently been plotted out at the time of writing) forever. This is probably the passage that Robinson drew his source material from.
The problem is that he completely ignores something from three paragraphs earlier!
"This present Volume Three starts about seventy-five years later than the end of the last story in Volume Two - and a great amount of "Future History" has taken place between the two volumes [Volume 2 was 'Green Hills Of Earth', Volume 3 is 'Revolt in 2100' - edit mine]. 'Green Hills' ended with [pay attention now -] the United States a leading power in a systemwide imperialism embracing all the habitable planets."
Scudder's rise and the end of interplanetary flight came WELL after what Robinson proposes. Robinson broke canon.