Sharp has recently rolled out a new 5.5 inches 4K IGZO display with resolution up to 3840 x 2160 pixels and pixel density at 806ppi. In contrast with other high resolution and high pixel density display such as the Samsung Galaxy S6 and the LG G3, the high pixel density 4K IGZO display has an indistinguishable picture quality from the naked eye. Hence, it is unsure that how does a mini 4K display can enhance visual experience of the user and will only know when it is marketed worldwide.
Meanwhile, smartphones with 4K display could suffers if the battery technology does not innovate when it is implemented. For example, some smartphones in the market today with 2K display with less than 3000mAh battery has faced severe short battery life when it comes to durability. Nevertheless, this display is expected to be in production at 2016 where battery problem could no longer be an issue.