I found this information from the same site Anti-APTX4869 found preliminary M-16 news last year, and that news turned out to be true, so I'm betting money this is legit as well. I'm not Korean, so I'm going off of Google Translate here, but I'll give it my best shot.
Original text:
명탐정 코난 극장판 제 16기 - 『11번째 스트라이커』의 극장 개봉과 동시에 차기작인 17번째 작품의 제작이 결정되었습니다.
17기의 예고영상은 제 17탄 제작결정! 이라는 글자와 동시에 검은 바다 속에 떠오르는 배가 비추어진 영상이었다고 합니다.
"배"는 9기 극장판의 주제로써 이미 중복이 되지만 아직 정확히 어떤 스토리인지는 알수가 없습니다.
오늘 일본 현지에서 개봉한 극장판 16기는 16주년 기념으로 J-리그와 전면적으로 협력하여,
현역 J-리그 선수가 성우로서 출연하는등 세간에 많은 화제를 불러일으키고 있습니다.
대만에서는 이미 7월 개봉이 확정되었으며, 중국과는 수출관련 협상중, 한국에서의 상영예정은 아직 없습니다.
Translation: (well, more of just a summary of what the passage is saying)
The first line simply states that at the end of the sixteenth movie, the seventeenth movie was confirmed.
The second section is what's important. Apparently, something illuminated (presumably a ship) rises out of a black sea. The writer says the theme of "boat" is redundant (alluding to M-9), but there's no other news of a plot yet, so there's no saying how the movie will turn out.
The third section is all just basic stuff about M-16, no news.
(if anyone is Korean, better translations would be appreciated)
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According to comments, some people say it's a submarine, not a ship, that rises out of the sea.
Once again, this info is from KudoNet™, a Korean Detective Conan fan site.
Link:
http://www.anifocus.com/aflegacy/zboard/zboard.php?id=kudoNews&page=1&sn1=&divpage=1&sn=off&ss=on&sc=on&select_arrange=headnum&desc=asc&no=1224
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UPDATE: 10/15/2012
Link to announcement trailer --> http://www.youtube.com/watch?v=q--a6-n4RLw
UPDATE: 11/13/2012
First link broken. Here's link to HD trailer with French subs --> http://www.youtube.com/watch?v=_7xCKUdOl1I