Given how unprepared they seem to be on this one, I'd guess it'll be closer to a late December release than an October/November… but they've always in the past started advertising the next games in spring, usually starting in February.
Late december would be horrible from a marketing perspective. You want to hit November/early December for gathering the highest possible number of sales. In the west at least, since in many countries this period involves pre-holiday sales as well as most schools being out due to winter vacation.
Not sure how true this is from the perspective of this being a global release, but I can't think at the moment of any game as huge as a main pokemon game to release in late December.
Personally I'm just really confused about the output of information. Given they want a global release again with more languages there's no way they're that behind in development. They'd need at least 2-3 months for solid localization and loc testing to take place, and that's assuming they need all of that done before submitting the game to rating boards and such, which is about a month or so at least before release?
So they really can't be that behind the curve and they must have a lot more than concept designs at this point. Which is really confusing because of how little information they're sharing compared to X and Y…