As previously discussed, the MacBook Air has become so good that it’s going to continue to eat into MacBook Pro sales. Apple needs something to differentiate the Pro — especially if there is a 15-inch Air. That something could well be a laptop with a “Retina” display.
I don’t think the 15.4-inch MacBook Pro will get the Retina treatment first. The 15-inch MBP comes in two pixel formats: 1440×900 and 1680×1050. Sooner than later my guess is the lower-end 1440×900 will no longer be offered. You wouldn’t want the latest and greatest to be associated with something that will be EOLed. Besides putting lots of pixels into a bigger display is much harder.
I think the 13.3-inch MacBook Pro will get the Retina treatment first. This might not make sense at first. The 13.3-inch MBP has a 1280×800 pixel format. Doubling the horizontal and vertical pixels will get you 2560×1600. That’s not what DIGITIMES rumored. But if the rationale for a Retina display on MBPs is to distinguish itself from the MacBook Airs then the 13.3-inch MBA, not MBP, should be the point of comparison. The 13.3-inch MBA comes with a 1440×900 pixel format. Double that and you get to the rumored 2880×1800. And that’s what I think will be the biggest difference between the two 13.3-inch MacBooks.
Apple will certainly gain considerable experience with the rumored 9.7-inch 2048×1536 Retina Displays for the next iPad, but going from 9.7 inches all the way to 15.4 inches seems too big a jump. My guess is for the smaller, easier to manufacture, 13.3-inch MacBook Pro to get the 2880×1800 Retina display first. Distinguishing it from the 13.3-inch MacBook Air would be easier, too.
Update 2012.03.02: Richard Gaywood, TUAW:
The first is that in order to achieve, or even handily exceed, the threshold for a Retina display, Apple does not need to double resolutions on most of its displays. Far from it. It would suffice to boost a 27″ Thunderbolt Display from 2560×1440 to something around 2912×1638.
The second point is that people shouldn’t get their hopes up for how much better a Retina display Mac would be compared to the current offerings. The iPhone 4 was a huge step forward from the iPhone 3GS mostly because the 3GS’s screen was comparatively poor. Existing Macs have much better screens to start with, so any improvement will be much more modest.