When this puppy comes out it will be a hard choice between the 24-70f4 IS the 24-105, and the tamron 24-70 2.8 vc as they will all be around the same price. If you can get over the backwards zoom of the Tammy that's probably the lens of choice in this price range.
I'm guessing...the price tag 24-70 f4 IS is $1599?
I wouldnt be surprised by that pricing, but if this is the kit lens going forward I'd expect it closer to $1200 like the 24-105 and about $800 in the kit. So it won't make munch sense for anyone to pick up this lens in its own. The 24-105 is likely on its way out, which is too bad, it's maybe the most perfect travel/general use lens on the market.