Take emojis and stickers offline to real life.
Incorporate into messaging systems (Facebook, Viber, a new app just for this) the ability for users to “leave” messages, emojis and stickers at real life spots in the city. When the recipient approaches the spot, the system will either show him the message or guide him to the place (a game like hot-or-cold) and then show him. The spot can be a meaningful one, or just somewhere the sender knows the recipient will be like on route home.
You want to express your feeling at a certain moment using an emoticon, but none are quite right for what you want to express.
An app that takes a picture of you while you are trying to express your emotion. You look at the picture to see if you got it, and when you did, you ok the picture. The app then creates an emoticon based on that photo. It might do two or three versions, and you can send the one you like best.