Liam Robertson, who is usually a reliable source, has reported that the next Assassin’s Creed game will be set in Greece and release in 2019.. This is following the fact that Origins was originally set to have portions of Greece in the game (before the decision to focus solely on Egypt was made).
Ubisoft previously revealed that Assassin’s Creed wouldn’t return to a yearly release, so this one is definitely set to release in 2019 rather than this year. It’s also reported that the game won’t come to Nintendo Switch, but still only release on PS4, Xbox One and PC.