The thing that surprises me about this rumor is that a 15" MBA isn't part of it.
It will surprise me tremendously if next year Apple is producing an 11", 12" and 13" MBA.
If the 12" is real, I think next years line up is a 12" & 15" MBA, and I'm frankly WAY more freaking excited about a 15" MBA than a 12". That would mean I could finally step down from MBPs.
In that case, wouldn't a 14" MBA make more sense? You then have the high(er) end Pro at 13" and 15" and the Air at 12" and 14". That would allow them to make the case only slightly bigger with these screen sizes, so they will feel a lot more portable.