Why isn't it possible? If apple wants, they could put a 5K display into 4.7in iPhone 8.
And why isn't it acceptable? Remember this is a compact phone. There are still 5.2in devices like Xperia XZ big phablets like Huawei Mate 9 at 5.9in with Full HD. The resolution is nothing innovate or something you really need some new tech to do it, it just doesn't make sense if you have a resolution which is too high, but then sacrifice your 60fps at gaming and everything else which is graphics intensive.
