I'm days away from hitting the BUY button on a 2012 13" MBA Ultimate (i7/8/512) with ML and we now hear that the 13" rMBP is right around the corner... Great!? (in a sarcastic way)
So, if an Ultimate MBA costs $2,200 and a 15" 2.3GHz/8/256 costs also $2,200... How much will the 13" rMBP be? Could we get the 8/512 for let's say $2,400?
For me, this extra $200 would really be worth it. Let me hear you...
If you're torn between the fully decked out 2012 13" MacBook Air (a surprisingly popular choice in the Mac community, it'd seem) and the would-be 13" Retina MacBook Pro, I'm going to have to say that you ought to go with the former. My reasoning is this: after playing with the 15" Retina MacBook Pro, I can safely say that, if everything (in terms of apps and web content) were developed to take advantage of the retina screen, it'd be fist-fulls of win, but in 2012 it isn't. If you buy a retina display MacBook Pro (regardless of the physical screen size) most things as they run today will look pixelated and like crap and sadly, while apps might get their **** together, the rest of the internet (in terms of optimizing web content) likely won't. By the time retina is standardized, whatever retina MacBook Pro you could buy in 2012 will be on the verge of being obsolete (as in, unable to run whatever the modern version of OS X is at the time). For that reason, I'd say go with the souped up 13" Air as it stands today. Nothing you run on it will look like crap and with 8GB of RAM and 512 GB of SSD space, you're good for the long haul for sure. By the time you are ready to replace this machine naturally, maybe Mac software and Internet content will be more or less retina-ready.
I highly doubt there's a 13" rMBP around the corner. There are limits to what Apple can do in a 13" enclosure. Currently MBA is using all the space it has. A retina display not only requires more battery life, but also more computing power.
The 15" Retina MacBook Pro is designed to be able to run on the Intel HD 4000 when in battery-saving mode. Therefore, if a 13" Retina MacBook Pro lacked a discrete GPU, it, in theory, ought to still be able to function. Let's remember that a 13" "retina" panel would likely have fewer pixels to push than the 15" panel currently in use.
I see the rMBP as the replacement of the now obsolete (except if you upgrade) 13" MacBook Pro. I don't really see it competing with the Air.
It's very much clear that, especially while rocking a 1280x800 (instead of 1400x900 like on the 13" Air) in 2012, the 13" MacBook Pro as we know it today has its days numbered. Same with the non-retina 15". To call it now-obsolete, on the other hand, seems premature.
Also - they're not likely to butcher a product so shortly after the WWDC updates. I'd say we don't see an rMPB 13" until at least the Haswell refresh.
Apple unveiled the iSight model iMac G5s three months before replacing them with the Early 2006 Core Duo equivalents. (Though if memory serves, they were sold side-by-side for a month or two.) Apple is perfectly capable of repeating this sort of thing again with the 13" MacBook Pro (let alone with the 15" MacBook Pro as well). They clearly see the transition from Hard-Drive/Optical-Drive/Removable-RAM to integrated-everything as a substantial move and are clearly trying to take their time with it as they'd be morons to assume that, as stubborn computer users, we'd just roll with it overnight.