Even though earlier rumors suggested Samsung will adopt an LCD for the upcoming GS5 phone, it was later reported that the GS5 will actually adopt a 5.2" WQHD (2560 x 1440, 560 PPI) AMOLED panel. Today, at a display technology roadmap seminar, Samsung confirmed that indeed they are developing a QHD AMOLED panel.
Samsung will not stop at 560 PPI. The company is actually planning an even higher density panel - a UHD panel that will feature 860 PPI. It will be very hard to justify such a high density on a mobile device, but I guess it's a marketing race that is hard to stop. At any case, it seems that Samsung will be adopting the Diamond Pixel architecture for those high resolution displays.