I rather like my reaction GIFs and discussion threads. What I want to see is a modern IRC with these features, and an optional per-channel/per-server message persistence to deal with not knowing what happened while you were away, or while the mobile IRC app of your choice was killed by the Google/Apple background task manager that only allows you to dodge it with proprietary push support.

This is Slack, mostly, kinda.

Slack also smacks of terrible usability, and is proprietary up the wazoo. There is no way to automate anything on it unless your organisation gives some approval.