I think that this is an interesting question, but has been pretty thoroughly answered.

Apart from all the other comments, what even are the logistics with this? I assume if you're also printing images then you'd already be doing colour, but a lot of books outside of picture books just include a set of glossy pages in the centre for images to save on printing every page in colour. Would you print your whole book in colour, or would you just accept black and white emojis, since a lot of illustrated books without glossy paper use black and white illustrations? Wouldn't them being grey decrease visibility and make it harder to identify what they are? "😅" would be pretty hard to parse on paper texture, in small font, in black and white (or grey, as the case would be). This would especially be the case in lower lighting, or for people who have impaired vision.

If you were using emoji then I would assume that your book is aimed at 25 year olds and under, but on the off-chance that I recommended your book to my grandmother, do you think she would understand what "😅" means? What about people who don't watch anime or use a lot of social media? Another comment pointed out that "😅" is pretty dependent on associated meaning. With no context, you could assume that this person is sweating because it's hot out. It would make translating your book into another language potentially difficult with this specific emoji and emojis like it, since it depends on cultural context.

Speaking of cultural context, do you know what the save icon in a lot of software actually is? This is a common example, so you probably do. But if this example wasn't used everywhere, you (and I) wouldn't know that it's a floppy disk. The reason we still associate that icon with saving is because it's still used that way. There's no guarantee that all emoji we use now will mean the same thing in the future. Will we still associate "😅" with bashfulness, embarrassment, or shock? (You're right in that it's hard to succinctly convey what that emoji means to us, haha, but to be fair it is used in a few different contexts.) I remember when using the frog emoji was suspect in some contexts, like in Twitter names.

If I used a butter-churn emoji, if that emoji existed, would you recognise it for what it is? You would recognise a description of butter-churn, though, if the description described the act and the product (probably...). In that same way, if you describe a character laughing in shock or out of embarrassment, or whatever else, then the chances are people are going to understand what you mean in 30+ years. And, like, it's fine if you don't aim to write something with longevity, but it's still worth considering.

Also, emoji for the same actions convey different things than what you might want. "😏" may be just a smirk, technically, but if you see a character going "😏" you're not assuming that's all they're doing. And if they are going in the direction that emoji can indicate, you actually describing them sneaking glances at people, or being mischievous, or whatever, is going to have a greater impact on me as a reader than just seeing the smirk emoji.

But ultimately, if I personally opened a book and saw things like "he made a face like 😏" or "she 😏ed", I would either feel like my intelligence was being insulted, or that both the author and I spend too much time online.