While the mockups are good, the specs don't seem to have much credibility.
First, I don't think that Apple will reduce the screen resolution to 1024x640. The technology is definitely there to keep the resolution at 1280x800 for an 11 inch screen (or 1366x768 for 11 inch pc laptops), but seeing as how 16:10 is pretty standard for most mac laptops, Apple will probably try to keep a 1280x800 resolution.
Second, I doubt that Apple will switch to Intel HD graphics. They showed that with the 13in Macbook Pro and will probably stick with that decision for the upgraded Air. However, this means no Core i3 or i5 processors, still Core 2 Duos (possibly with an Nvidia 320m).
There is one exception to this though, and that's if they redesign the Air. With a redesign that has a constant .5-.6in thickness, they *might* be able to engineer a 13 inch Air with graphics switching technology (think of a slimmer 13 inch pro without a cd drive and without as many ports), but I doubt that any 11 inch Air would be able to take advantage of that.
Ideally, there would be 2 new Macbook Airs this September.
An 11.6 inch Air with a Core 2 Duo, 320m, possibly 4gb RAM, and 1280x800 screen starting anywhere from $899 to $1199 (without SSD), around $1200-$1400 with 128gb ssd. ("The smallest/thinest/lightest mac ever").
That leaves the 13 inch Air... if there's no redesign, expect similar specs to above starting at 1199-1399. If there is a redesign, a 13 inch Air with Core i3 or i5, 4gb RAM, 320m, and same 1280x800 screen. ("Portable Professional Performance"). The problem with a redesign of the air is that eventually (once Apple removes cd drives from most mac laptops, probably in late 2011 or early-mid 2012), the 13 inch Air and 13 inch Macbook Pro would merge into the same machine (which would probably just be called the 13 inch Macbook Pro).
Thinking rationally, I don't expect a redesign, but I can always hope for one.