Notice how these new lenses are SUPER SLOW? The lie we're being sold is that IS makes up for the 1-stop loss. I predicted this trend years ago--that Canon's lens development will go in the direction of slower-aperture, IS designs that are more profitable because they don't need tighter tolerances or more expensive optical designs, but the price tag is "justified" because, oh, wait, it's got IS, as if that will totally make up for the slowness.
I'm frankly sick of this. Especially in light of how even a company like Sigma can make a sub $1000 50/1.4 lens that beats the pants off of anything Canon or Nikon has *ever* made at that focal length, and has people comparing it to a $3500 MF lens from Zeiss.
These new lenses will be overpriced (the L being at least $2100, I guarantee it), and will still under-perform even though it will be a little better in the corner sharpness over its predecessors. At such short focal lengths, almost any IS advantage is nullified by the fact that unless you're shooting something that's completely stationary, the shutter speeds at which IS would be relevant would result in subject motion blur.
It's dangerous to make predictions man! You are off on a quite a few here. We now know the price - $1199. And we do have a CR2 letting us know that a 2.8 UWA is on the way.
Now as to all lenses being slow? This one is pretty false, Canon is filling gaps in it's lineup, and yeah that does include a few slower lenses with IS - why, mostly to satiate the video folks out there (and yes, some still shooters want it) - and - it fills a few more price points too. Those on a budget now have a trinity of f4, this doesn't eliminate the 2.8 trinity by any means (the 70-200 2.8v2 is still fairly new, and the 24-70 2.8v2 is very new - so now the question mark is will the 16-35 get it's v3 or will it become a 14-24?)
The part you are right on is your $2100 figure, but it's for the wrong lens. The new UWA 2.8 will probably be at around $2100, like the other new 2.8's....
As to sigma - apples and oranges. Sigma mostly specializes in lenses, they don't have anywhere near the overhead as canon does - or nikon for that matter. Also, while the ART series is the start of a change for sigma from cheap low quality glass to moderately priced better IQ glass, they still have issues, mainly in their AF systems. Reading through the forums I see lots of mixed messages about the 35 and the 50 ---they beat the pants off the canon offerings when the AF hits, but AF consistency is a big issue that sigma needs to fix.