Add the ability to "Pin" messages (either to the bottom or side panel). Allows you to write a message and then discuss it without having to find it again when you want to re-read the original.
People have been requesting this feature for at least 5 years. What's the status of it? Everyone I know is migrating to Slack, not necessarily only due to pinning, but also other things like feedback and general improvements.
Pinning messages and inbox items is discussed in this suggestion:
I'd suggest focussing discussion and votes in that thread.