What amazes me is that people look this new 24-70mm and discount it against the 24-105mm and discount it because of the extra 35mm and price.
I am looking at this lens and from what I see it may be superior to the 24-105mm in ways that matter to those of us who spend the extra money to buy L lenses.
While there are those that buy the L lenses for weather sealing and low light abilities, I think if you compared everything together IQ is going to be the top reason.

What I am hearing about the new 24-70mm is it has Macro capabilities at the long end. So to speculate a bit, the IQ and resolution will have to be very good at the long end to make this worthwhile.

If you look at the MTF charts side by side and compare what you see is that the new 24-70mm isn't any better than the new 24-70mm II or the old 24-105mm. You gain nothing by going with the 24-70mm f/4 for landscape and wide. However, if you compare at 70mm you see that the 24-70mm f/4 is showing the best performance on the charts compared to the 24-70mm II and the 70-200 f/2.8 II, the new 24-70mm f/4 is better than all three.

I think what we are going to get with this lens is the best IQ performance of any zoom in the 70mm range, average performance on the wide end and the ability to do extreme close ups at 70mm. The question to weigh will probably be; vs the 24-105 do we give up 35mm and $600 for the close ups and IQ, vs the 24-70mm II it will come down to f/2.8 vs IS.

I will be real curious to see how the reviews come out for this lens.