Post updated:
A brand new Sigma patent spotted by Nikoneye.com shows that Sigma is developing a new range of f/1.2 fast primes. And thanks to an update we got via our reader Mistral we now learned that these lenses are designed for Micro Four Thirds (and not APS-C mirrorless as previously guessed). There are three lens versions: 14mm, 24mm and 35mm f/1.2.
Sigma google translated text explains why the lenses need to be fast:
Although many interchangeable lenses with a larger F value than F1.4 are provided, in order that they may make depth of field still shallower, an interchangeable lens whose F value is smaller than F1.2 is desired.
But a patent is just a patent for now. They may never will really bring such lenses on market.