One thing they have to do to win me over is to deliver the lenses I listed (or something similar), deliver consistent quality And add weather sealing. It is unthinkable for me to sell my L-glass for anything without weather sealing. The current Sigma lenses I have now are bought more from curiosity than need.
I have to agree with Eldar on this particular point, I have the 35 Art, like it, use it, but, without weather sealing, for my type of Imaging (Dust/Rain/Snow), no weather sealing handicaps the Lens so I tend to bring it out in optimal weather conditions.
But, the Sigma 35 Art is other than the lack of weather sealing, a very good Lens, in most areas better then my Canon 35L, I look forward to getting the Sigma 50 Art, I suspect it may well perform better then my Canon 50f/1.2 L but not as well as my Otus 55, but it will have a reasonably reliable (hopefully) AF feature.