According to BMW chief engineer Frank Isenberg, there?s just no place for an open-top M2 when the M235i convertible already exists.
http://www.automobilemag.com/news/report-there-will-not-be-a-bmw-m2-convertible/

http://www.automobilemag.com/news/report-there-will-not-be-a-bmw-m2-convertible/