With a FF body, IS is not needed for the 24-70 range unless you are doing video....
Well maybe that's true for the way you shoot, but it's possible yours is not the only shooting style on the planet. Throw someone creative a new tool like IS on a 24-70 and chances are they'll start delivering shots that were not possible to achieve without it. Every new option delivers potential for new creative possibilities.
From the day that film cameras stopped being mainstream, we have had a rapid, almost endless succession of new and exciting developments in what is still a very young, though rapidly maturing industry. I'm talking about the digital revolution and it HAS
been a revolution, now maturing into brisk evolution.
24-70 with IS? Bring it on. Also bring on all the developments still in R&D and also those not yet invented. We live in exciting times.