Google Stadia is launching in just a few days, but it looks like a fair number of its features will not be available at launch. Most of these features are related to multiplayer gaming and include State Share, Crowd Play, Stream Connect and Buddy Pass. Additionally, there will be limited functionality for PC, Chromecast Ultra and the wireless controller.
https://www.notebookcheck.net/Google-Stadia-will-be-missing-quite-a-few-features-at-launch.442819.0.html