I myself fail completely to see the market for this lens. Sure, if they are going to 'force it down your throat' as a Kit lens, maybe... but lets see who would choose this lens:
- For versatility, the 24-105 has the same widest aperture, and considerably longer reach.
- For speed, you have any of the 24-70 2.8 options (including the mI) in Canon and even other brands.
- For those 'amateurs' looking for a good lens, they are probably on an APS-C sensor, and therefore have MUCH better and less expensive choices like the 17-55 f2.8 IS .
Again, if it would be on the $1K range... then I can see this as a good lens which several people will chose: newer better optics vs. the extra 35mm reach of the 24-105 could be interesting, but not paying TWICE as much!!! Never! As mentioned, for APS-C sensors, the shorter focal range zooms are actually more in the 'normal' range, the 17-40 included, which sells for about $700!.
So this lens is certainly best for FF cameras, and those having them will either pay the extra for the 2.8 versions or go for primes. I really only see them ditching the 24-105 (which would be purely from a marketing point of view as it is a fantastic lens! they would really be ill-treating customers if they dropped it!) and forcing this new 24-70 f4 as a kit lens.
So, IMHO, I see a purely commercial move that will involve some very 'wrong' (from the customer point of view) decisions. I see no other 'great' scenario for this lens. The 17-40 is better for most landscapers and crop sensors, the 24-70 mI, mII and Tamron are better choices for professionals and the 24-105 is a better choice for an all around lens.
I really fail to see this lenses purpose as well as others (and I don't think the 24-70 mII is a great success from a technological point of view, its a great success commercially because people just *have* to have the latest and priciest, but I believe, as others, that Canon 'failed' with that lens - which doesn't mean people are not buying it... perhaps we are talking about different types of 'fail' here - )