lol.
A: HBO already had the manuscript, what little there was.
B: Season 6 already covered pretty much all of winds, for the characters on the show. I'd wager that everyone, except perhaps Sam, is well into book 7.
C: They are delaying the start of shooting, because they need colder climates to shoot against is valid
D: Despite the season being shorter (7 episodes vs 10), the production is so massive at this point, it will take just as long to film those 7 as it did to film 10 in previous seasons. As an example, The battle of the Bastards, not the episode, just the actual battle, about 18 minutes of episode 9? Took 24 days to film. As we're now in the stories conclusion expect less "2 characters sitting around dialoguing filling up space" and more shit getting done.
E: As such, I expect them to film for 7-8 months like they have for every season so far. They usually start in July and end around February or so, then post production, editing and cgi etc, continues until the individual show airs. If they wait until say, September to begin shooting, then I expect the show to be delayed until June or July