I had five Sigma EOS compatible lenses, and none of them worked on Canon DSLR's. 400mm, a 105,, Mac50, a 28mm f/1.8 and two zooms. This was due to the poor reverse engineering that Sigma did for the Canon system.
Of the five, only the 105mm Macro could be upgraded with a fix, and they charged my over $100 to make it do what it was supposed to.
I'd be concerned that some new Canon AF system will once again break all the Sigma lenses. The Art Lenses might have downloadable firmware if they are current models, or maybe not. At any rate, I am avoiding them, particularly with the new Dual Pixel AF systems coming out. There will be changes in the AF system, and who knows what issues third party lenses will have?