Google is updating the Hangouts Chrome extension in the very near future, as they have just posted an announcement to the Google Apps Updates blog that states they will be ushering in a new version on August 31st of this year. As far as what's going to be new with the "new" extension, the image above should paint a pretty clear picture as it displays that the look and feel of the design will be pretty similar and almost identical to that of the Hangouts Chrome app, with the biggest thing being that the new extension will integrate the multiple chat windows into one window.
Google's aim here is to make conversations with the extension that much easier to see so that using it to talk with your Google contacts is a much more smooth and seamless process, which sounds like just as good of a reason as any to give the extension a facelift. Google notes that all users will begin to see the new version of the extension from October 17th, although it will also be possible for users to opt into using the new version before then, as Google will make it optionally available to existing users on August 31st alongside new users of Google Hangouts. If users choose to stick with the current interface option from August 31st, October 17th is also the date that the current interface will disappear and the new one will replace it automatically.
While anyone who is using the Hangouts extension currently will continue to be able to use the existing interface up until October 17th, any new users who download the extension and begin interacting with it from August 31st will have to use the new interface by default, so if you want the chance to see what the old interface is like, using the extension before the August 31st date is recommended. Other recent changes to Hangouts include the addition of the "shruggie" emoticon in the Hangouts application on Android, as well as the removal of Hangouts on Air from the Hangouts app while it was shifted over to YouTube Live.