Actually, you're asking two questions here, since the thread title is "Will their [sic] be retina MBA in future"Do we anticipate that there will be retina displays in the airs in future
Yep, they already have one. They called it the 13" MBP with Retina Display.
This is the correct answer. The rMBA is already an ultraportable. Introducing a rMBA would make little sense as it would cost as much as the rMBP and probably be close to the same size. The specs on the rMBP are close to what an air is. There is nothing to differentiate the two. If someone wants a retina ultraportable there is no reason not to just buy one today. Apple makes one.
That's not true, the MBA has an 11" model (and just over 1/2 the weight of the 13" retina), quite a differentiating factor in my mind (the 11" is the one I have and love, though I would also enjoy it with a higher resolution display). The technology, though, is indeed advancing and now with the removal of the optical drive from the MBP, I wonder if these two lines might be merged in the future because they will (I assume) at some point be able to produce an Air with rMBP specs, or looking at it the other way, an rMBP in an Air chassis (either would work for me), but I don't want to give up my 11".