I'm 95% sure we'll get a release date at Gamescom, during the last ATR they said Gamescom would be the start of the games ''promotional run'' (or something to that effect). The date will be around April 2016. SE tends to like there early in the year launches, they won't want to launch in the holidays with the Fallouts, Call of Duty's, Halo's etc....

The game is very far along at this point and SE have to get it out relatively soon if they want KH3 and the FF VII Remake to launch this console generation :S

An on stage demo has already been confirmed, I think we get a story trailer with the release date aswell.