The main problem with emojis (usage of them aside) is that while they are characters, they do not work in the same way as other characters. Smileys are composed of symbols right at your fingertips. Native emoji keyboards are severely lacking - typing them is a lot different than text. The worst part is that while fonts exist since forever, the emoji generation forgot all the engineering put into it and no font tooling works with emojis. Whatever font setup you have, it goes down the drain once emojis are in the text, because emoji glyphs come not from your font setup, but from within the rendering application.