Emoji picker: dito as above, but you’ll also have to create a kirbytag so you can convert it in the front-end I think.
Formatting in a field in the backend: you’ll have to roll-out some kind of wysiwyg editor field. Fwiw my experience with wysiwyg is that it’s often more a hassle then a gain (cross browser issues/poor formatting/…). I kind of like the simplicity kirby provides, and I hear the same from my clients. Because of this, I like this enhanced textarea plugin, have a look at it.
Don’t know if they still work, but if you need something like this, they may serve as a basis for your own development. But I agree with @bvdputte, don’t really see a gain.