Burek on 17 June 2015
So, according to Shu Yoshida http://www.engadget.com/2015/06/17/an-intimate-chat-with-sony-playstation-shuhei-yoshida/
SEGA gave permission for Shenmue III on condition that it gets successfully Kickstarted. And Sony's involvement was possible only after that was the case. Of course, a free on-stage advertisement certainly helped the game reach its goal in record time.
