This is still under review by the feature team.
This item is still on the backlog.
We are getting closer… the team is almost ready to rollout MacOS notification support internally for testing – we hope to have it to the public by the end of this quarter.
Our group is experiencing the same issues. It's surprisingly hard to figure out when someone adds to a channel. There's no red notification badge in the dock and the proprietary notification bubble doesn't show up with the list of notifications that come from literally every other app on my computer.
We’re currently working on defining a compact mode experience. I will post more details when we have more to share.