Sigma Austria posted a teaser on their Facebook page about a new lens that will be announced on February 23rd for the 2016 CP+ show in Japan. Here is the translated text:
Today, we can pre-announce another world premiere - the [official] presentation will take place on February 23rd. At the moment, we can just tell you that it is once more something 'sharp' and 'fast' [in the sense of large aperture]. Please tell us about your favourite focal length. Keep writing us busily and stay tuned.
Your Sigma Austria team