Google Assistant's app integration is going to get better with Android 8.0 Oreo, as it looks like Google is prepping the software to where app developers will be able to make better use of it in a number of ways. Third-party apps will eventually be able to interact with Google Assistant that will make it possible for the app to initiate an activity through Google Assistant when the user is inside of the app. On top of this Google seems to be setting it up so that this new integration will work with other digital assistants beyond Google Assistant, such as Amazon's Alexa app or Microsoft's Cortana app.
As of right now the functionality isn't something users can readily access, but it is on the way. A new string found within the Android Developers website code listed as startVoiceActivity describes the capability for an interaction to be started by voice so long as the application supports Android 8.0 Oreo. So therein lies one of the caveats. Not only will a user need to be on a device running on Oreo, but the app itself will also have to support Oreo for developers to make the use of the function, which means depending on when Google rolls this out and makes it possible for developers to start adding this integration, the list of supported apps might be small.
What isn't clear at the moment is what kinds of activities developers will be able to use Google Assistant for. Presumably that might be at the developer's discretion, and although Google may end up providing a predefined set of possibilities, it would make sense for developers to have a wide variety of potential actions that they could integrate with their apps to make them more intuitive and to give Google Assistant some more value for the user. The fact that Google seems to be opening this new activity up to other digital assistants might also suggest that Google really wants developers to make use of the functionality, though it will surely also bolster Google Assistant too. Those who use Google Assistant on a daily basis may want to keep an eye out for new integration from their favorite apps, as the functionality may show up sooner rather than later.