I think some of the folks are right in thinking this will be another kit lens.
The new full-frame will be geared toward the prosumer market and a small, decent lens will work better for them. I have the 24-105 and even though it is smaller than the 24-70 2.8, it is still a big lens.
And there is no reason to think canon will not offer two kit versions of the 6D, like they do with the 7D with the 18-135 and the 28-135.
A company the size of Canon does not make decisions without researching their target markets. I have worked on advertising for Canon in the past and they do their homework.