It will be really interesting to hear how the 24-70 lens has been improved. There had been rumours that there would be an IS version, but that does not appear to be the case.
This lens will probably be offered as a "kit" lens with the (hopefully soon-to-be-announced) successor(s) to the 5DII (5D3, 5DX, 3D or whatever), but for those who already own the current 24-70, the question will be whether to upgrade.
My speculation (and it is only a speculation) is that if the lens really uses an 82mm filter now (instead of 77mm), we are not just looking at a minor upgrade, but a major redesign to improve what some people consider the biggest problem with the 24-70 lens - the focus plane curvature. If they could reduce the weight at the same time, I would be very, very happy, but I guess that is too much to ask.