I will be honest, I haven't came around to using XMPP myself yet, but I am pretty sure you are able to do all of those things, at least with the help of extensions. Here's the XMPP standards that are currently stable or experimental:
Files/Images:
- XEP-0363: HTTP File Upload [Stable]
- XEP-0446: File metadata element [Experimental]
- XEP-0447: Stateless file sharing [Experimental]
- XEP-0448: Encryption for stateless file sharing [Experimental]
Emojis/Stickers:
- XEP-0444: Message Reactions [Experimental]
- XEP-0449: Stickers [Experimental]
Looking at clients, I see various ones that have at least some of the features you are looking for (especially file and image sharing, I haven't found a client that has explicitly implemented the stickers specification yet, but Movim seems to have them):
I would give it some more time. It seems those features are in development, but this is essentially an alternative to Matrix that is more standardized. It's a widely adopted and integrated protocol, so I don't doubt the features you are looking for will become more fleshed out some day.