Although this would be absolutely fantastic, I don't see this happening for many reasons.
It's already been done in the past (Sony had a 13" laptop with 1080P years ago), it's just never been in a popular device like MBP. Apple's relationships with their fabs are so good, that the fabs are willing to justify the high costs of producing such a high-risk and expensive move to the new manufacturing lines. It's one thing doing it for a small niche population but it's another thing doing it for Apple's 10+ million customers.
The technologies we have now are capable of doing this, the problem is the yield. The fabs can't produce enough good screens to meet Apple's quality requirements (no backlights, no dead pixels), but it is possible to get there quickly.
iPhone 4 was the first mass-produced high-res monitor. Samsung already mentioned that they want to release 2560x1600 in a 11.6" tablet according to the latest rumor from BGR.
If Apple opts for a 2880x1800 screen, wouldn't a 2560x1600 screen be much more practical?
It has nothing to do with the resolution but more of the pixel density. Apple wants to make it easier to scale up by doubling the pixel density. For one black pixel pixel on the current screen, the Retina display would create 4 tiny black pixels to show one black pixel to the user. It looks much sharper beacuse there's more details. You can't use 3 or 2 pixel to do the same. They won't look the same, so you have to double it two ways, (2*2). The current native resolution on MBP is 1440x900, so Apple has to double it to 2880x1800 (1440*2 x 900*2).
On the 15", it would be 2800x1800, for 17" it'd have to be 3840x2400.
Also, the application of this concept is very unlikely for a MacBook Pro. How do we expect to cram a 2880x1800 display in a 15.4" form factor when we can barely fit a 2560x1600 display into a 27" monitor? Not only that, but the amount of power necessary to power such a high resolution screen will be tremendous and would drain battery life.
We don't know anything about how it is developed, there may be new technologies that optimized for power uses. It may be a bit more power hog than the current screen but there are certains techniques that can be done to mininize the power requirements. Apple may have also developed new battery technologies to increase its density without adding more weight.
Intel HD Graphics will never be able to support such a display all the time. It struggles already with 1600p; how does one expect it to work for a 2880x1800 screen? This would mean that for such a "Retina Display" to be used, Apple would have to put a GPU in the MacBook Pros for regular use instead of the Intel IGPs.
If this rumor is true, it'll be in the next MBP with Ivy Bridge's CPU with iGP 4000, it'll support up to 4K resolution just fine, Intel confirms this. It doesn't require that much to push that kind of resolution. Gaming on the native resolution is a different story, that's where the dGPU come in. For typical OS usage, it doesn't require that much power.
Finally, the colors would be absolutely terrible. The reason that MacBook Pros are praised for their displays, despite being a mirror, is that they have a fairly high color gamut and color accuracy. On the other hand, the iPhone 4 was revealed to have a color gamut of around 65%. Which means the color quality of the display will suffer, even when properly calibrated.
Apple wouldn't sacrifice this many things just so it can quadruple the number of pixels.
Sure, it would. Apple has already shown in the past few years that it'd be willing to sacrifiic to carter for the regular users, not the power users. For regular users, they don't care about having high color gamut, they never cared for it in the past and they certainly won't now.
