Google has added Zoidberg and Corgi easter eggs into Hangouts with the latest version of the app on Android devices, and anyone who is on version 23 (or any versions following this most recent one) will be able to activate these easter eggs with a quick couple of messages. Like similar easter eggs in past versions of Hangouts, all the user has to do is type / followed by the term to get the easter egg to show up, and in this case for zoidberg, that term is simply zoidberg. So, type /zoidberg and you'll see an ASCII version of the character pop up on screen in the chat box.
This is all well and good, especially if you're a fan of the series Futurama where the character comes from, but the corgi easter egg is a little more animated and thus probably a little more exciting. Typing /corgis will result in a little animated corgi pup running across the bottom of the chat window UI, similar to the way Google implemented the pitchforks easter egg some years ago which resulted in an angry mob running across the screen with, you guessed it, pitchforks in their hands.
So far these seem to be the only two changes that have come along with this Hangouts update, but there's always the possibility that there will be more, and there have probably been some changes to fix bugs and just improve the overall user experience. That said any other additional features wouldn't likely be any large sweeping changes as Hangouts isn't Google's main chat application for Android anymore now that it's trying to push Allo. This is only more evident by Google's push to add more fun and excitement for users to stay engaged with the new chat app by way of working to add in a new feature called activities, which will let users essentially play games like Chess and Quick, Draw! with friends inside of the chat. Google also tends to make announcements about larger feature changes, improvements, or additions, and there hasn't been any announcements about Hangouts in this regard, so if there are any larger changes meant for Hangouts at some point, those will probably be coming in a future update.