Contact lists.

Your contacts can set an #avatar and it will be respected.

Why can't we select our sound notifications? Or ringtones?

Empty avatar gets replaced by a unique generated one. Like an #identicon.
This exists for #sound ! https://github.com/jasonbot/identijingle

Why is no messenger using that?

With a single sound for everyone in #Element I have to waste time checking every unimportant message.

#xmpp folks, is there a #xep ?

#jingle #identijingle #messengers #communication #matrix