That sort of hyper-abbreviated writing has largely disappeared thanks to spell-check, predictive autocomplete, and so forth.
Emoji can certainly stand in for text, and I see plenty of comments and text messages that consist primarily of emoji. But just as often they will accompany text to add personality or mood the way ASCII smilies or textual kaomoji always have on bulletin boards.
(I'm sounding like a right grumpy old git here)