Some old, familiar apps may no longer appear in the tray, where you expect them to be.

For Unity 2D, the story is long. Now, there may be other new apps you want to install, but what about the old ones? 

Many of your old familiar programs no longer show up in the new “indicator” area; unless you fool it. Some systray icons for QT-based programs such as Skype and VLC are automatically converted into indicators by sni-qt. Wine, Java, scp-dbus-service and the Update-notifier are whitelisted by Ubuntu, but you can whitelist all applications.

In Dconf-editor, navigate to desktop > unity > panel
And to get the equivalent of the Systray in the Notification Area for all applications, change the default list to [‘all’]. Or you can add program names individually, in single-quotes, comma-separated by coma, e.g., 'Wine', 'Skype' etc.

To reset the list, the default value is shown in the Dconf-editor  ['JavaEmbeddedFrame', 'Wine', 'scp-dbus-service', 'Update-notifier'] or click on “Set to default” in dconf-editor, bottom right.
