You should see the Air getting a retina display. Apple now has 3 notebooks, each addresses a specific niche, none address all 3 niches let alone even 2:
Pro: Tons of horsepower, the go-to device for Fortune 500 media creation, publishing, packaging.
Air: The least expensive MacBook, tons of legacy ports, strong horsepower, the go-to device for Fortune 500 IT departments whose executives insist they don't want a Windows machine.
RMB: Expensive, low value quotient, experimental, a flagship model for the brand and a demonstration of what Apple is capable of for the traveling executive who has a minivan and wants a convertible in the garage for the weekends.
No magazine publisher is going to drop the Pro, no IT department on a tight budget is going to slot the RMB, and no frequent flyer is going to drag around a thick and heavy Air.
Everything you saw in the past from Apple, all the tweaks and changes and revisions, it's when they only had 2 notebooks. They just expanded the line and are differentiating, no different than BMW taking its narrow, staple 3 Series and morphing it into a 2 Series and a 4 Series, we live in a world where choice is important to consumers, boilerplate no longer works.
Apple will focus on the Air and the Pro. The RMB is very new to the market and isn't a priority. The RMB is predicated on A) form factor and B) nonchalance towards processing horsepower. Skylake doesn't affect A or B, it's not happening, at least not now.
BJ