When people rag on Sigma AF issues, they should at least differentiate between past issues and the current issue seemingly affecting the new 50.
The big set of AF problems that seemed to have plagued Sigma glass forever appears to come from poor and/or incomplete decoding of Canon's lens protocol, and the art line seems to have resolved this issue for now. Thanks to the usb dock Canon can't pull any further "the new camera ain't done until Sigma glass won't run" stunts.
The problems that seem to have affected Eldar and Viggo appear to be plain manufacturing issues, that are not uncommon when brand new products are introduced. These issues shouldn't become the new normal either, and I sure hope that Sigma's manufacturing lines get their act together quickly.
PS: If people draw a straight line through 35 and 50 price points to determine the expected price of the new 85, then I wonder what price people would expect for upcoming wide angle glass in the art line ...
Wide angle speculation is a lot tougher as it's not just a simple 'non-L price is low and L price is comical' sort of Canon landscape. In 35, 50, 85 Sigma has a sweet spot around $900-1000 where an L competitor (hell, L beater) will do really well.
But in wider FL, there are a lot of high quality options and more price points. Besides the two T/S lenses, there's the 24/1.4L, the 24 F/2.8 non-L, as well as
And don't forget that the landscapers don't explicitly need AF, so Zeiss goes from 'exotic tool with limitations' in standard focal lengths to a very reasonable L alternative at a number of wide focal lengths.
Add all those lenses up and it's just a murkier market for Sigma to wade into. They can and will do business there, but they need to clearly define what they are going after: make a 24/1.4L killer for $1000, make a 16-35 F/4L IS killer for $800, make a 16-35 F/2.8 killer for $1200, etc. The first and third on that list are right in Sigma's wheelhouse, but the second would be a tough one to pull off -- the 16-35 F/4L IS MTF charts look quite impressive for the dollar.