Currently Google hangouts have two set of customers
1) Corporates (B2B)- Google hangouts is already monetized as a part fo gsuite
As a PM I can think of enhanced features on hangouts and sell to B2B customers.
I am going to focus on individual users.
Individuals for personal use: Not monetized yet. Free product.
What functionalities available on Hangouts : Chat, Call and Video
Individuals are unlikely to pay as there are free substitutes available. ( Whatsapp, messenger)
Potential monetization avenues:
1) Integrate with Google maps: Customers can realtime chat with businesses. Free for customers. Paid feature for businesses.
2) Build value added features such as voice/video over low bandwidth internet. Charge for heavy users.
3) Video calling - Real time voice translate features for people speaking in different languages.