Rumour is Canon making a IS version to update their 24-70 next. I am not a fan of the mk2, I prefer the mk1 where the barrel zooms inside the hood.
I would wait for reviews. Previous Sigma 24-70mm lenses were not that great, especially poor Bokeh.
I like the Sigma Art Primes and I think the 50-100 Art is a nice lens, as is their 24-35 F/2.0 is an impressive piece of engineering, 2 useful focal length with a wide aperture so I have no doubt actually the 24-70 will be very good.
As for the Canon, I know optically that lens is better than the mk1, for me, the 24-70 is now my spare lens and the mk1 servves that purpose just fine.