This is in internal testing. I don’t have exact timing for you, but wanted to let you know it is coming!
Yes! Please use the built in Notifications in MacOS and not the custom built one currently use. I guess the same thing goes for Windows.
While you are at it please make use of the Badge feature in MacOS to show the number of unread things. (like is done in the iOS Teams app)
Kaylin Norman-Slack commented
Came here to say this. With the current banners, it's easy to miss them (possibly due to their size relative to any other programs that one might have open). Having the Action/Notification bar update with them occasionally if they haven't been check might make it easier for team mates who don't see the posts immediately. I know for myself personally due to the notification bars it occasionally sends to my main screen, I'm much more likely to check there than in my system tray.
System provided notifications in general, like in macOS as well ;)