I was sent an email late last night stating Canon plans to announce such a lens at PMA. I still don't buy it. The source also stated a few other lenses could be announced:
EF-S 17-200 f/3.5-5.6 IS
EF 24-70 f/2.8 IS
EF 100-400 f/4.5-5.6 IS (4 stop IS, twist zoom?)
EF-S 10mm Fisheye (sorely lacking in the canon lineup)
None of the current lenses are seeing any big price drops or perceived inventory shortages, so I have doubts any of them will be replaced yet. The EF-S 17-200 is a possiblity.
I do think there will be big lens announcements for Photokina when Canon announces the new 1D.
We had to buy a new camera to replace our beloved Canon PowerShot A95 and I have absolutely no complaints about the PowerShot SD780IS. I’m not a professional, just take pictures for myself and I still haven’t figured out all the features but it’s easy enough for the basics. I would (and have) recommend it.