According to the Egami Blog, Sigma has filed a patent for an 11-22mm f/4.5-5.6 DG HSM FLD Art lens. Below is a screenshot of the Google-translated patent presented on the blog.
Sigma clearly has the Canon 11-24L in its sights with this lens's development and, considering the Art line's heritage, it will likely be released with a much more attractive price compared to Canon's extreme ultra-wide.