I could be wrong but I don't see Apple putting in some sort of Retina screen in the Air until Intel gets iGPU performance (5200 Iris Pro) or slightly more into the ULV chips. Perhaps the IGZO Retina would give similar battery life but would still be rocking the HD 5000. Also if they kept the same resolution number scheme the Air displays, this would be the results:
11: 2732x1535 (270PPI), the highest Apple notebook PPI to date.
13: 2880x1800 (256PPI), same overall pixel count as 15 but in a smaller footprint making for much higher PPI.
At that point given how impressive MacBook Airs are in performance vs Pro's, who would ever buy a 13" rMBP. Sort of a dilemma for Apple IMHO. Perhaps they will Mac a 12" and redesign all the Pro's to taper but so hard to figure out what Tim Cook will do next.
Far as waiting, if you wait till 2014 then you will be asking yourself what about 2015... I'd say buy now and start saving up for 2015. As I don't see Broadwell making their way into the notebook line till late 2014 or early 2015.