@SlackHQ Like the change to the direct messages, the icons make it easier to spot a person's channel. The problem is that it is harder to see if someone is online as the green dot (I use the dark theme) is harder to see.
Could you make the icon be outlined with the active color?
While we have no plans to change this at the moment, we really appreciate the feedback! 
For now, you can try changing the color of the active presence so it's a bit easier to see it. You can do that in Preferences > Themes > Colors.