Look, this is bollocks.
The EF-S 17-55 f/2.8 IS USM is already one of Canon's best lenses (and one where Nikon fails to exercise any competitive pressure). It's ridiculous that it should be a candidate for replacement.
How about introducing a new lens to actually fill a gap? An EF-S 55-150 f/2.8 IS USM, for example. Yes, yes, I know about the various 70-200 Ls. Too big, too heavy, too white. I want smaller, lighter, crop sensor lenses. Something to slot in above the 17-55 would be fabulous.
And how about a few crop sensor primes. A 35mm f/1.4, say...