I know you guys don't want to see comments like this, but I feel like with the evidence I've gathered, my comment should justify that Square did indeed hype this specific event up for KH fans, only to give us less of what was offered.
If you recall, after the E3 2015 trailer of KH3 was shown and released, it was revealed that we'd be getting more info about the game in both the North American and Japanese D23 events. But, after getting a world reveal for the NA D23 event, we were led to believe that we'd get more PUBLIC info AND footage of KH3 (with articles like these: http://www.ign.com/articles/2015/08/19/new-kingdom-hearts-3-footage-to-debut-at-disney-d23-expo-japan-2015), because 1. we were able to watch a livestream in which Big Hero 6 was revealed for KH3, and 2. the trailer shown at the D23 back in 2013 was released (a day later after the event, mind you). So most of us naturally thought, "what's going to stop them this time?".
A release would have been possible for the trailer shown at this year's D23. Unfortunately that doesn't seem like it'll be the case, considering the statement later given by the Square-Enix EU Community Manager and this passage, which reveals the same details we were given by the attendees on Twitter:
"For the latest Kingdom Hearts III footage, an event-exclusive movie was revealed, featuring the full version of the conversation between two people playing what looks like a chess match (the one that begins with “Have you heard of the Ancient Keyblade War?”). Both seem to know something, but they do not utter it. They are friends, but they also appear to be rivals… their relationship is quite palpable."
...Yeah, at this point I think a release of the trailer isn't happening. However, Square might have their own good reasons for releasing trailers like what we got in 2013 and at E3 this year rather than anything shown privately. I'd like a story trailer myself, but I wouldn't want it to show too much. Maybe the developers are waiting until they can put out a spoiler-free trailer. At this point, who really knows?
Anyway, I apologize for the long comment (and also for linking an IGN article as a source even though there are other sources which also post about the info reveal date), but I felt like throwing my two cents on this situation here.