Well you can't be surprised, can you?
In what only felt like an inevitability, Google has put out an announcement that Hangouts On Air events will no longer be tied to Google+ and will be completely contained into YouTube Live instead. It'll be a hard break on September 12, where Google+ will no longer be able to create Hangouts On Air and any events scheduled for the future will have to be manually recreated on YouTube Live.
Just one less reason for big media outlets and personalities to use Google+
It doesn't take much thought to realize this makes a whole lot of sense from multiple perspectives. Not only has Google+ usage continued to decrease as YouTube continues to be as strong as ever, but the idea of live video streams from your phone and computer being tied to YouTube while live Hangouts were tied to Google+ just made things confusing. With the move to YouTube Live, it will be even easier to keep everything contained into a single platform rather than crossing streams.
If you want to look at things from a bit more cynical (albeit increasingly rational) point of view, you'll also note that this means businesses and media personalities will no longer have to go anywhere near Google+ in order to have a live show or interview using the Hangouts On Air technology. And considering the notable exposure that provided for Google+ as a platform for discussions and groups, this is a pretty big move away from Google+ in terms of promotion and marketing.