There are quite a few categories in the app stores that cross-channel attribution is crucial for them. Travel and shopping are the best examples - users tend to use various devices before making a purchase. However, the Google Stadia launch proves that games, and probably other categories in the future, will need to have better clarity of the entire user journey, across all devices. This for sure will be the next evolution for digital and mobile marketers, and attribution solutions need to support it.
For deterministic models, mapping out user journeys across multiple screens requires:
1. Device ID / Google Play referred
2. Cookie ID / Customer ID
For probabilistic matching, various types of fingerprint methods (Battery, size, RAM, wifi, etc) are used.
As an example, an app-to-web conversion path (highly popular in eCommerce and Travel) looks like this:
One important note - privacy and security play a big part in cross-channel attribution. It is vital to understand the legal implications of following a user across different screens.