The Whiskey Lake 15W parts you reference are just 14nm++ parts that replace the i5-8250U, i5-8350U, i7-8550U and i7-8650U 14nm+ parts that were released last August. Quad with GT2 graphics. Apple wasn’t interested in them last year, but sure they could go into a machine meant to be a MBA replacement.
Regarding a possible new 13”, I don’t think the way to get a $999 MBA replacement is to introduce a larger version of the $1,299 12” MacBook. The $1,299 MB or $1,299 nTB MBP could be reduced to $999, or the MBA in its current form factor can be upgraded with a better processor and presumably a retina screen.
Or, a completely new 13” machine is introduced to replace both MBA and the nTB MBP. But they already have the current nTB, why a new machine? This is what doesn’t make sense about a new 13” machine. Apple always said the 13” nTB is the replacement for the Air.
How does a brand new machine become a better $999 replacement for the MBA than the current nTB—a platform that has easily sold 10-15 million units (nTB+TB) already.
I think they might have arrived a bit too late for the June 2017 MacBook release, and the MacBook may now be in a prime position to replace the MBA now that we've had 3 generations for Apple to recoup the development costs.
Currently the nTB is priced distinctly above the MBA range, but if Apple are to drop Thunderbolt 2 machines from the range something has to fill the $1000 Mac price range and I think it would be odd for Apple to simply refresh the MBA with Thunderbolt 3 ports and keep the existing large bezelled TN non retina display.
A price re-alignment may be due for the 12" model, especially if they introduce as 128Gb SKU which they would have to if there is to be a 13" model with 128Gb SKU.
Replacing the nTB with a model called the rMB 13" might be as simple as re-using the nTB case design with a 15w CPU with non-Iris GPU where Apple can save a few dollars. Apple could also shave a few more dollars off the cost if they were to use USB-C ports (at Gen 2 speeds - 10Gbps) which I believe would be possible on 300 series motherboards paired with Whiskey Lake CPUs.
It might even be feasible for Apple to spend engineering resources to allow 4 ports if they were all USB-C (Gen 2/10GBps)