According to the image of the Galaxy S4 successor, the device will be 133.3 millimeters long and supports a screen of 5.25 inches which corresponds to previous rumors . We also see a QHD Super AMOLED screen type, which would mean that the Galaxy S5 indeed features a display with a resolution of 2,560 x 1,440 AMOLED. The pixel density (ppi) might come down to 560ppi
Seriously though, is it worth it? I mean, it'll take tons of CPU and battery to run that many pixels that you can't even see. I mean, the entire point of "retina" displays is that you're not going to be able to see the pixels, but there is a point where adding more pixels just won't make any difference than on a spec sheet.
Even when TV manufacturers makes LED TV's slimmer and slimmer there is still an actual use case for those superslim sets, and 4K video on a 60" TV is still not retina resolution. Well, it is when you're sitting in your couch, but then again, so is 1080p.
It's like the design team at Samsung said "We'll make the resolution of this 5" device the same as a 27" monitor, can we?" and the hardware team answered "Sure we can, but.." - "THEN LET'S DO IT!!!"