My prediction has been that they will release a 13" Retina MacBook (not an Air), and then they would drop the price of the 12" Retina MacBook to US$999 with a new cut down 128 GB model. The Air would then just get discontinued.
So, unless they surprise me and release an ARM Apple A12 Bionic based 13" MacBook, all the MacBooks would remain dual-core Intel Y series.
That makes sense to me. There’s no way they can introduce a 13” retina laptop thats cheaper than their 12” MacBook and lighter than the 13” nTBMBP without killing off both those models.
The 12” MacBook has paid off its R&D by now so could have its price dropped, and a whimpy 128GB model introduced to drop it further.
Bumping up to a 13” MacBook with an extra port and similar form factor then gives a new way to maintain the high margins on the machine most people will lust after.