This item is still under consideration by the feature team.
Similar to Slack, Fleep, Skype, and others, the systray icon should change if a new, unread message arrives. Part of the problem is that the Settings > Notifications area of the Windows app doesn't have very many options. I would like to see an option where I do NOT get a pop-up notification on the lower right corner. Some messages may be private, so I don't want someone walking by to be able to see them. Instead, I should be able to DISABLE pop-up messages and get a systray icon change that visually tells me there are new/unread messages -- again...similar to Slack, Skype, etc.