At a special Dark Souls III event in Tokyo, photos of which can be seen here, the Japanese release date for Dark Souls III has been confirmed for March 24th, 2016. Judging by the comments of people who can translate Japanese, there will also be a Playstation 4 exclusive network test available before launch.
No word yet on the international release date, but I feel it's safe to assume it will be pretty close to the same time. Dark Souls launched about two weeks sooner in Japan than abroad, but Dark Souls II launched two days later in Japan than abroad.
With a release date that close, I'm sure we'll be seeing a lot more about Dark Souls III soon.