I know this is a mobile app so people can generally pretty easily put in regular emojis, but Lemmy allows for instances to have custom emojis and I know of at least a few that do. So, having an emoji picker to let people make use of those seems like a good idea.
Also, said custom emojis currently embed the same way as regular images, such that in comments where they are used in-line, it can break up the text in a way that both looks bad and can make things harder to read:
I'm not 100% sure if there's a way to fix the second one since the custom emojis are at the end of the day just images afaik, but if so that would be nice.