I would take it in a moment. The main advantage of my current MBA 13 is the flatness and absence of weight. I have it with me daily to work. In the past, the white MB was after a while too heavy.
I have an option to get rMBP paid by my employer. I am waiting - doubts about the 700g more weight and reports of screen problems.
If Apple can get a MBA 15 out, lighter than rMBP, even with a normal panel, say 1080x1650 resolution for my presbyopic eyes...