The "screen is the same as in 2015" part isn't true. The resolution is, but the gamut, color accuracy and brightness have all been improved. TrueTone was also added in the 2018 revision (although one might not care much for that).
4K would be nice and might come in the next redesign, but there are other parameters to look for in a screen aside from resolution. Display quality is not only a matter of bigger numbers.