I disagree with the thought of the crop sensor cameras going away any time soon.
When (becuase it's not 'if' it's 'when') full frame sensor cameras drop down into the sub-$1000 range and thus into the mainstream consumer price range, APS-C will die off.
What evidence can you possibly point to that would indicate that full frame sensor cameras are going to drop below $1,000 in price?
It takes much less imagination and there is much more evidence to support the opposite conclusion: when the rapidly narrowing gap between APS-C and full-frame sensor quality becomes virtually indistinguishable full frame sensor cameras will go the way of 8x10 view cameras, 4x5 Speed Graphics and Rolleiflexes.
Now, don't get your panties in a bunch. I'm not suggesting that full-frame will become obsolete in the next two-three years. I'm just saying that there is more evidence to support that conclusion than the idea you're suggesting.
There is absolutely no objective reason to think that APS-C is going anywhere, or at least that it is going to be done in by an older and more expensive format. All the trends point toward shrinking, not growing, sensor size technology. (And, for those protesting that full frame will always
be better quality than APS-C...well...junkyards are full of technologies that were better quality, while "good enough" technology laughs all the way to the bank.)
I would certainly hesitate to predict what cameras and lenses will be like in a decade. Perhaps the SLR with its interchangeable lenses will still be around, but it's entirely possible that we'll all be carrying around tablets that zoom digitally with resolution far beyond anything that can be found in either full-frame or APS-C cameras today.
Instead of this goofy "I've got a bigger sensor than you" discussion let's get back to the OP's original point.
To the OP: I'm not sure about the specific lens you suggest, but I certainly agree that the Canon lens division has not done justice to the APS-C market. They've left the innovation to third parties who are poaching customers.
The three higher quality APS-C lenses that Canon makes all have their problems. The 10-22mm and the 15-85mm are too slow. The 17-55mm is better at 2.8, but it's neither wide enough at the short end nor long enough at the long end. (I'm hoping they come through with a 15-65 mm 2.8, which would be a killer lens)
I'm generally a defender of Canon, but I am really having some doubts about their lens division. I'm just not sure it shares the same vision as the rest of the SLR unit. Seriously, look at the lenses they've chosen to introduce over the past few years: updates of massive supertelephotos that fill a tiny niche market, a nice quality 70-300 mm L zoom that the jury is still out on whether there is any market for it; a specialty fisheye zoom that also fits a narrow niche audience and which they can't even seem to bring to market anyway.
In the meantime the SLR division brought out the 7D and 60D, two higher-end APS-C bodies, and aside from the 15-85 mm zoom, there have been no corresponding lenses released.
Imagine the sales jump they'd have if they introduced an EF-S 100-400mm f4? Lighter, faster and about the same price as the current full frame 100-400. Sports and wildlife photographers would be lining up to buy that lens and 7D combination. (Now before all the nitpickers start picking away, this is only an example of the creative options that the lens division could be following if they were to get with the EF-S program like their SLR brethren have gotten with the crop sensor program.)
I have to wonder if the lens division needs more forward-thinking management.