i don't think it is coming to the 15" EVER.
i had a compaq laptop (x1000, a thin fast laptop) with 1920x1200 in a 15" screen.
it was legible only if you were directly in front of the laptop and i'm in my late 20's. so if you plan on using a stand (icurve or whatever) and using an external keyboard, be prepared to squint.
also, before apple would jump to 1920x1200, it would make a separate jump to 1680x1080 in the 15"
the 15" started as 1280x800 then got an upgrade to 1440x960
the 17" started as 1440x960 then got an upgrade to 1680x1080, and only just now had the option of 1920x1200.
apple will likely look at sales of the 1920x1200 17" and decide carefully whether or not to offer the option of 1680x1080 on the 15"
I just don't think thaqt 1920x1200 is a mass market resolution, and apple would have to start with a 1680x1080
(ps - i know my pixel count for the vertical is probably inaccurate, but that is because adding the isight into the laptops changes the number of pixels vertically relative to previous isight-free laptops and pc laptops)
Very well summed up. 1920 x 1200 on a 15" is just silly. Especially at my age...not like I'll see those pixels