For reference, a 2/3" (1/1.5", whatever...) sensor should be about 1 full stop better than the sensor in my little Elph 500 HS. Now, my Elph is f/2 at 24mm-equivalent and if the new camera is indeed 2/3" and 28mm-equivalent and f/2.5, it would only be a little bit faster than my Elph is already at maximum wide angle.
I'm actually pretty impressed with what Canon has done with the tiny sensor in my little Elph, and I am a 5D and fast prime owner so I do have a solid reference point. But for this camera to be interesting to SLR owners, in my opinion, it has to be as fast as, or faster across the whole range than something like the S90/95/100 cameras are, since they are already f/2 at the wide end, are pocketable, and have bigger sensors than the one in my little Elph. To do that, f/2.5 at the wide end probably won't cut it with a 2/3" sensor. So it either needs a faster lens or a bigger sensor. If it really has an almost-APS-C sized sensor and f/2.5 at the wide end, well that's something.