I think it will be a great addition for wedding photogs, but as a walk around a little too large....and zoom range a little too short on FF.
It looks to be incredible, and it is incredibly priced as well. It'll be the definitive 24-70 zoom of ALL manufacturers, besting Nikon's counterpart, Sony's counterpart, and killing the new Tamron 24-70 VC in IQ alone.
If they'd included IS the image quality would have taken a slight hit I honestly believe. I'm sure they researched it, tested it, and developed the lens according to those factors. I will never get it, opting for the 24-105 or it's replacement if that ever comes to fruition. I need IS on a zoom, no doubt.