Yeah it could possibly head that way. I think if you keep in mind that companies like Apple are looking ahead at what's coming down the pipeline in terms of next gen CPUs etc.. they might indeed be foreseeing that a couple of generations down the track the core M (or whatever it morphs into) is going to functionally cover the same ground as what they were aiming for with the Air. So the entire notebook line could be more decisively split into two ranges using the most suitable processor type - extreme low power consumption for ultralights, and the best mobile performance processors available for the "Pro" range.
I think it's also possible that the Air could persist for quite a while too. If they've decided it has hit the end of its development run (i.e., no major redesign in the works, no retina display etc), then they might do what they did with the original plastic MacBook when it phased out. Give them a very significant price-cut so as to make them even more compelling entry level models, they'd basically become Apple's netbook or low cost "education" offering. From there, they might continue to give the Air cursory updates, increasing the RAM and storage as-shipped so as to stay current and possibly keeping the CPU up to date, ish. And then see how long it continues to sell for.
Of course it's entirely possible that this isn't at all what's on the playbook, a revamped Air range with retina could make an appearance after all.. although such a machine might sit a bit uncomfortably in between its two sibling ranges. I guess we'll see huh?