I think it's more for those of us with the 24-105, we're all going "meh, this lens does nothing for me." Those with the 24-70 f/2.8 (either version) look at it with disdain/envy since it's f/4 and they need f/2.8, and it has IS which many of them would love.
Nearly all of us are a bit confused, because unless it's quite a bit cheaper than the 24-105 for something like a 6D bundle, why should Canon go ahead with yet another lens that seems less useful than one they already have that they've been making for years and many, many people are happy with. If indeed it is quite a bit cheaper, even if it's around the same IQ as the 24-105, it makes a lot of sense. If it's a bit cheaper or about the same, and much better IQ than the 24-105, maybe we have a new FF kit lens and the 24-105 is going away without an update Either way, I think it really depends on the price this will be as to how well it will be received.
Sounds pretty reasonable. Just like the 70-200mm range you pay such a whack for that extra stop of light.
I would have thought, though, that we could expect better IQ than the 24-105. I'd be surprised if it was not quite a bit better.