Google Chrome developer François Beaufort recently posted a Chrome OS screenshot on his Google+ page that shows a new messaging service. According to Droid Life, this new service could be the one that unites all of Google's web services. The right side of the image shows a pop-up notifications bar that has a design like Google Now on Android devices.
It displays notifications from Google Voice, Google+ and maybe even G+ Messenger, which definitely qualifies it as a united messaging service. There're no additional information on whether this messaging system was seen on Chrome browsers yet, so for now we can only assume it's for Chrome OS. However it should be pointed out that Chrome OS is built like Chrome, so the new feature could easily appear on Google Chrome.
Droid Life also noted that Google+ users (who are probably also Google fans) commented on the screenshot saying that they have high hopes that this will be the service that unite all notifications from Google's services into a single messaging center.
Judging from how Google has neglected Google Talk in the past two years, and how Facebook is aggressively trying to get in on the messaging scene, it seems like a good time for Google to introduce a new unified messaging system. If this new system takes off, we might even see it on Android devices in the near future.