I wonder what resolution a 13-inch retina display would be. I would guess it would double 1280x800, which would be 2560x1600, the same resolution as a 30" display. And I wonder what the scaled resolutions would be, I'm guessing 1680x1050 and 1440x900.
Hopefully it has a decent video card. I like that the 15" rMBP can drive 3 monitors (2 off of ThunderBolt, 1 off of HDMI) + laptop display for a total of 4 displays. Dual Thunderbolt ports is good in general, especially when the dongles for Firewire, Ethernet, etc, don't have a passthrough. Hopefully it doesn't lose that feature. I'm also hoping it has a 768GB SSD option, but I imagine it will as I don't think Apple wants to miss out on the profit from that option.
I'm hoping to not need a Mac Pro anymore with my next MacBook Pro purchase. Not sure about 15" or 13", but both sound appealing. If the 13" loses too many features, I would probably go 15". 768GB is a squeeze coming from an almost full 1TB system partition on my Mac Pro, but I could do it. I'm probably going to wait until next year for Haswell and also to see what the new Mac Pros are like just in case. Maybe they'll have 1TB SSD option in the rMBPs by then.
I'm also considering get a regular non-retina MBP (maybe even a refurb/used 17") instead and outfit it with a 1TB HDD and the largest SSD I can afford (install via Optibay or equivalent), so that I have a ton of storage and don't need to dock that often, but it just seems like I'd be going backwards if I don't get a retina model and the extra portability seems nice.