UPDATE: Sigma announced a terrific new 18-35mm f/1.8 lens! This is the fastest zoom for DSLR systems ever made! The only similar lenses are the Olympus 14-35mm f/2.0 (here on eBay) and the Olympus 35-100 f/2.0 (here on eBay). Both priced well over $2,000!
Sigma didn’t release any official info about the price and the mount. All other details can be read at Sigma Photo website. This is an APS-C lens and I really hope it will come for A-mount too!