The Google Developers Blog recently detailed some of the projects that are currently in progress by Area 120 (Google's internal workshop for experimental ideas) on virtual reality advertisements.
Google notes that both developers and users alike have been asking for a way to implement advertising experiences in VR experiences and have been working on a way to bring this request to life. The first idea from Google's Area 120 is to introduce an interactive cube that can be interacted with—via a tap or a gaze—to reveal a skippable video advertisement inside of a virtual environment.
The cube for viewing virtual reality advertisements is described by Google as easy for developers to implement and customize. On the other side of the spectrum, it is also said to be non-intrusive for users.