I'm not sure that this isn't just a possibility that Canon patented when it was designing full-frame macro capable standard zooms; it seems to me that what we actually got was the 24-70 f/4 IS.
Does Canon need a lower price kit lens? That depends upon the price of the camera body; it seems that kit lenses tend to fall into the "cost ~25-33% of camera body price" bracket. Currently the 24-105 is selling for $1100/£650, which is fine for the $3200/£2300 5D Mk3, but a bit high for the $1750/£1350 6D.
Canon are also deeply Nikon focused (and vice-versa), Nikon have a cheaper kit option with their new 24-85 f/3.5-4.5 VR at $2296. Whilst the 6D has the better lens, for the uninitiated $2450/£1925 is still more expensive than the Nikon kit. On top of this, I'd be willing to bet that Canon is making a lower profit margin on its 6D kit than Nikon is on their D610 kit. This would leave them vulnerable to any price cutting promotion from Nikon, so there is probably some justification for a cheaper kit lens option, however boring to forum members!