Exactly. The 13" MBA just doesn't really make any sense any more. People are still buying it, but they are, IMO, ill-informed or showing poor judgement. I guess the silver bezel and a 10% price difference are deal breakers for a few...
This would only add confusion to their line up. I'm thinking they're doing the exact opposite and are going to make the decision process clearer for consumers.
11" Air is often said to be too small, 13" Air too close in form factor and price to the rMBP 13". Arise the ultra thin and super light 12" MBA, kill the previous MBAs (and cMBP), and everything is much easier for most consumers.
12" rMBA (ultra thin and light; road folk machine)
13" rMBP (everyone's machine)
15" rMBP (pros machine)
Trying to explain the full differences between a 13" MBA vs 13" MBP to Joe Average is just an exercise in frustration. Better (in Apple's view) to just make the decision for them. [Which they do all the time and is the cause of a lot of angst amongst Apple users who actually do know a bit and for critics of Apple in general.]
I think the choice between MBA 13 & rMBP 13 is not as easy as you think. The longer battery life and 20% less weight of the MBA is an important factor for many people, as well as the price difference. The MBA screen isn't great, but then the native resolution of 1280x1024 on the rMBP is also somewhat lacking for a modern laptop (yes I know it can scale, but "retina" mode still offers a relatively small screen real estate). CPU speed appears to be very similar between both models, particularly if you choose the i7 in the MBA.
Personally I think the choice is not that easy and Apple wants to differentiate the products more. If the current MBA 13 gets a retina plus the same RAM and the rMBP loses a bit of weight, they become essentially the same machine, give or take a couple of ports. I think your suggested line-up is the most likely.