Is art not valuable? Is it not worth paying for?

Obviously random emoji is not the Mona Lisa, but having pictures of your friends making funny poses or faces etc. certainly increases the value of a conversation. It's also completely optional; not being able to use such emoji won't negatively impact your experience. It will however make you really jealous of all your friends that can use those emoji, and FOMO sets in until you too join the club just so you can be the first to react with a funny emote for the situation at hand.

I also like having GIF profile icons.

Paying for cosmetic features has been, traditionally, one of the monetization models in gaming (which discord is inherently intertwined with) that ends up the least scummy.

What I find irritating is the absence of what Chinese/Korean/Japanese apps have: a curated sticker market where the platform takes a cut of money that goes to the IP holder (brand or artist).

No one said they're an innovation. Just that people value them.

You're not paying for emoji, your paying for an incredible product that provides a lot of value. Emoji is just one feature they hold back to tempt you to pay for the amazing thing you have been given for free.

It sounds greedy when you word it "paying for emoji" when in reality they are incredibly generous for holding back no core functionality from free users.

Emoji are in the sweet spot where if you can’t use special emoji you don’t really care, but some people find them shiny enough to pay for. It’s not innovation, but it’s definitely a perfect target for monetization.