In a recent interview with IR, Sigma representative confirmed what they already mentioned few months ago - the company has no plans to introduce a mirrorless interchangeable lens camera for now:
Q: We are seeing a lot of momentum with mirrorless or compact system cameras in general, and we are excited to see you continue to release great lenses for those mounts. There is an interview with someone from Sigma China a little while back that got a lot of coverage when the representative was reported to say that Sigma had no plans for its own mirrorless camera system. Can you confirm whether that is true?
A: Currently, we're not planning to make a mirrorless camera, because we're prioritizing support for existing systems, our SD and DP cameras. We have to take care of our existing customers. But that doesn't mean that Sigma will never make compact system cameras in the future. Right now, it is true that we don't have any plans to do so.