I will start with the note that Apple certainly does not want MBA to get further into MBP territory than they already are. That being said, I believe it's very possible to make the MBA faster, having a great battery life and being equipped with retina 14" screen without gaining weight, size or thickness. Maybe even implementing one additional thunderbolt/usb port (there is enough space for that on both sides, not to mention the back sides). Obviously retina uses more power, but why not use ultra low power Core M (4.5W) which will be utilized for basic stuff (energy saving), and when/if there is demand for more processing power (say Core M gets ~80+% load after you open more resource hungry app), Broadwell high perfomance side (~26W) would kick in along with the low spinning fan. Overall concept very much like the Exynos 7 Octa (8 core mobile CPU). It's a complicated design, but Apple had lots and lots of time to make it possible, and they are surely capable in cooperation with Intel. This kind of notebook would no doubt hurt the MBP sales for the time being (there is room for improvement for MBP as well), but it would surely be a big step from Apple redefining 'netbooks/ultrabooks' once more, and isn't this what matters the most at the end of the day? It's been quite a while since Apple brought up something special (last time that probably was back in the beginning of 2010 when iPad was introduced).