A platform was not announced, but the end of the teaser trailer shown at the event reveals the developer to be Cygames Osaka, which Cygames opened in May 2015 to focus on PlayStation 4 development (and is still recruiting).
Cygames has yet to upload the trailer to its YouTube account, but we have a stream-recorded version below. (Update 08/24/16: The official upload has been replaced below.) It shows a mysterious girl, pictured above, falling from the sky onto a city, also pictured, and the text, “She had a dream, embraced in the disappointment and regret of when the awakening arrives.”
A release window was not announced.