Man, I was really looking forward to buying this for a work computer but the lack of any 16 MB RAM option and Quad Core I7 option (not even BTO) at all has me rethinking. The lack of integrated graphics figures in there too, but that I was already prepared for.
So now I am sort of questioning the value equation for this machine in its current form. You can already get a MacBook Air with 8 MB of RAM and a Dual Core processor (albeit I5 only, and with a lower clock). With that machine, you give up a Thunderbolt port, but that is not a huge problem given the daisy-chain-ability. You also give up HDMI for easy projector connectivity, but that can be solved with an adapter if you really need it. And of course there is the obvious lack of Retina display. However, crucially for my purposes, both machines can drive two Apple Thunderbolt Displays.
True, configured similarly (equivalent RAM and SSD, fastest MBA processor, slowest rMBP processor) the two are only $300 apart. So, this makes the Pro look a little sweeter. However, the form factor and sub-3lb weight of the MBA arguably puts it into a whole different league as far as portability, even compared to the new sleeker, lighter enclosure of the new Retina Pro. This is especially true when you consider that you can go down to the 11" MBA and not lose a thing (other than screen size, oh and the SD reader - NBD) vs. its 13" sibling. Now you have a barely 2lb device that really is not that much less powerful than a 13" rMBP.
If you could get the 13" rMBP Pro with the same processor and RAM (and GPU, really) as its 15" sibling (similar to how the 11" MBA can be spec'd up to match its 13" sibling, as I mention above), it would make the machine much more attractive. But, as it stands now, I am sort of thinking I will either step up to the 15" rMBP, or just go with a loaded-up 11" MBA. The mid-sizers don't give me the right capability-to-portability ratio.
(Oh, and just to be fair I'll mention one more thing the 13" rMBP can do that the MBA can't - it can run two low cost ~$350 Korean 2560x1440 displays (I believe) due to it's two Thunderbolt ports. But I am really loath to take that gamble.)