omg I just did the same thing! I've been lurking on this forum for 5+ years when planning a trip, but have never actually posted. I was assuming late fall meant like Oct, or that the opening would get pushed back a couple months for whatever reason. I haven't been to Disney in years and booked a trip for 8/31-9/8 hoping for low crowds and hot weather (I'm one of those people that doesn't mind temps >90 degrees). Luckily my family is actually Star Wars fans, otherwise I would be more upset. I guess it's kind of a blessing that we got such a good deal at Pop Century + Dining Plan for this time(?)
Obviously most of the people on forums like this are Disney enthusiasts and probably only reflect ~10% of the visitors, if that. So I guess it depends if the more casual visitors will book during this time... There's a lot of factors like school, work, cost (maybe hotels will be more now), and it's hard to say what the crowd will be like.