According to a recent report from Kotaku, the next step for this series will be a "dramatic departure" from previous installments. And yes, from the looks of it, the game will take place in ancient Greece.
Following a lackluster response to Assassin's Creed Syndicate in 2015, publisher Ubisoft announced that it would take a year off of the core series for the first time in a decade to regroup.
Earlier rumors suggest that Assassin's Creed Odyssey will feature both a male and female protagonist, see players fighting against Greek mythological creates and will be set after the events in Assassin's Creed Origins.
It's worth pointing out that reports are conflicting about whether you play as Bayek, his wife, Aya, or new characters altogether. Now we might know even more, including what Assassin's Creed Odyssey will have to offer gameplay wise, and even when we might be getting it! Although the previously-annualised series had skipped 2016 in the wake of 2014's disappointing Assassin's Creed: Unity, it's likely that this one will be out this spring, returning to the yearly schedule for which the popular franchise has always been known.
I've reached out to Ubisoft for comment.
Finally, Schreier states that Odyssey is slated for release during Ubisoft's 2019 fiscal year, which ends on March 31st, 2019.