It appears that pixel density on smartphones will get even denser as Sharp has announced its newest 5.5-inch 4K IGZO panel with impressive 806ppi pixel density.
The new Sharp 5.5-inch IGZO panel will have a resolution of 3860x2160 which adds up to 806ppi of pixel density and since it is based on a conventional RGB matrix there will be no issues with sub-pixel rendering, although that probably would not happen considering an impressive density of the panel.
Unfortunately, making, or rather mass producing such panel is a bit tricky so Sharp does not expect to have it ready for customers before sometime next year but it certainly sounds impressive.
Source:
GSMArena.com.