What Heughan meant is that while Season 3 would air later than its usual spring release date, Season 4 is likely to air a few months after the Season 3 finale. It is possible that Season 4 could air in the latter part of 2017 all the way to early 2018.
The delay in the airing date has something to do with the tons of editing and post-production work needed to be done after filming is done.
The production team has already confirmed three casting additions to “Outlander” Season 3. In addition to David Berry, who shall play the role of Lord John Grey, John Bell and Wil Johnson have been taken into the TV series as well.
Bell would play the role of Young Ian who is Jamie’s cousin. His character is described to be a young lad who has the tendency to get into trouble. Ian is also an adventurous boy who exudes a whole lot of charm.
Johnson, on the other hand, shall be playing the role of Joe Abernathy, a friend of Claire Fraser, played by Caitriona Balfe, from Boston in the 20th century who shall also be her confidant regarding her time travel secret.
Joe is also a friend of Claire in the medical school. He is described as intelligent and charming and has a great affection for Claire. They shall reportedly have a long-lasting friendship but it is not clear how Jamie would react if he learns about this in the 18th century.