Would by a 14” immediately. 13” is just a bit too small. 14” is great for travel and usability.
I also think that it's the 12" models that are for the chop... plenty of opportunity for a 13" that's smaller than current 13" models... and the air is hardly portly anyway. Bigger displays in smaller bodies is what users want now, no more squinting into tiny displays as a trade-off to get true portability.
So... 13" + 15" + 16.5" is what I'd like to see make up the range.
And the Pro versions need proper keyboards... or I'm keeping my old Air.
I think the 12" MacBook will disappear in this shuffle, with 14/16" Pros, and the iPad Pro going to a single 12" SKU as the bottom of the MacBook line as the first foray into ARM based laptops. There is just so little difference between the iPad Pro and MacBook 12 (other than the iPad Pro is actually MORE POWERFUL) that there is no need for a 12" SKU. If anything, even the MacBook Air 2018 obviates the need for the MacBook 12.