Our customers enjoy great apps and games from millions of developers, and gaming services can absolutely launch on the App Store as long as they follow the same set of guidelines applicable to all developers, including submitting games individually for review, and appearing in charts and search. In addition to the App Store, developers can choose to reach all iPhone and iPad users over the web through Safari and other browsers on the App Store.
Google offered no comment about Stadia support via iOS, but a Microsoft spokesperson sent over the following response.
Our testing period for the Project xCloud preview app for iOS has expired. Unfortunately, we do not have a path to bring our vision of cloud gaming with Xbox Game Pass Ultimate to gamers on iOS via the Apple App Store. Apple stands alone as the only general purpose platform to deny consumers from cloud gaming and game subscription services like Xbox Game Pass. And it consistently treats gaming apps differently, applying more lenient rules to non-gaming apps even when they include interactive content. All games available in the Xbox Game Pass catalog are rated for content by independent industry ratings bodies such as the ESRB and regional equivalents. We are committed to finding a path to bring cloud gaming with Xbox Game Pass Ultimate to the iOS platform. We believe that the customer should be at the heart of the gaming experience and gamers tell us they want to play, connect and share anywhere, no matter where they are. We agree.