The official Who twitter account has just announced that the series won't be back until 2020. It's getting ridiculous now, I can't believe Chibnall wasn't able to make back to back seasons, especially given the massive gap between Capaldi's last season and his first, and it's not as if he's running another show in the same way RTD and Moffat were. I really hope he leaves after season 12 anyway as the scripts haven't been up to standard, and we get someone in who can run the show properly.