With the release of WotLK Classic, the latency bar is no longer visible within the default UI. Additionally, the game menu tooltip was not updated to display the latency.
For this initial version, the latency numbers get added to the game menu button's tooltip. Color coding for high latency may be added later.
Thanks to Swiftwoof of Frostmourne for the bug report on the official forums.
Update: With the September 9th hotfixes, this addon should no longer be necessary.
"Latency and other performance information is now visible in the tooltip of the Game Menu button." (source)
