The display is only part of the story. You could save some battery life with an e-paper display sure, but you still have the CPU and radio grinding away at the

The display is only part of the story. You could save some battery life with an e-paper display sure, but you still have the CPU and radio grinding away at the battery. The ultra power saving mode on my Samsung phone is a good example, it throttles the CPU, sleeps the radio aggressively, restricts the phone to only running a few basic apps, and turns off most of the OLED display. I can increase battery lifetime by almost a factor of 5 with that on. An e-paper display would save a bit more, sure, but the type of display isn't the only limitation to a low-power smart phone. You need to design the whole thing to work together to save power; changing one component isn't gonna be enough.