According to a press release dated 14 August 2015, the Swiss National Bank plans to begin issuing new banknotes in April 2016. The first denomination to be issued will be the 50-franc note, with the 20-franc note planned for 2017 introduction. The remaining banknotes will be issued subsequently at half-yearly or yearly intervals. The SNB will announce each new issue date well in advance. The issuing of the entire new series is scheduled to be completed by 2019.
Courtesy of Max Keller.