To add to the many other comments – 13" Air with a better screen.
It was the obvious product to build. It is baffling to me Apple cannot see this gap.
I see no need for two 13.3" models in the lineup and (from the outside) it seems they are deliberately holding back on improving the Air screen in order to differentiate from the Pro.
Maybe one way is to make the 13" more "Pro" (like its 15" sibling) with dedicated GPU and quad core processors. Of course the trade off is going to be weight/thermal envelope/battery life. Maybe the other way is to accept the technology isn't there to have a powerful 13" model, give up on the Pro/Air lines and just build a 13" MacBook.
There are other weird differences like the Air having native resolution with more usable pixels than the Pro. Of course you can scale the Pro to higher than 1280 x 800, but that defeats some of the point of the retina panel and causes some performance issues. A 2880 x 1800px panel would be better in the Pro as well.
By introducing the MacBook Prototype it has made the situation murkier rather than sharpening the vision.
For 2016 I'd like to see something like this with clear divisions between the lines:
MacBook Pro 12"
12.1" 2160 x 1440px IPS panel (1080 x 900px), 128/256GB SSD, 4/8GB RAM, 15W Core i5, Iris Graphics
MacBook Pro 14"
14.1" 2880 x 1800px IPS panel (1400 x 900px), 256GB/512GB SSD, 8/16GB RAM, 15W Core i5 or i7, Nvidia GPU
MacBook Pro 17"
17" 3840 x 2160px IPS panel (1920 x 1080px), 512GB/1TB SSD, 16/32GB RAM, 28W Core i7, Nvidia GPU
I'll have a think about the consumer options (mine is the 14").