As confirmed by Bloomberg, the current rules imposed by Apple to prevent service of game streaming to publish their applications on the App Store.
In practice, the rules of the store to prevent an app from the repository of games a third party, then no service as a GeForce Now, xCloud, PS Now, or Google Staff can publish an app for iOS.
The services game streaming online work hosting the games on servers in the cloud, essentially broadcasting in streaming a rendered video to the user device. This means that a title can be played on a mobile device, but have the fidelity of a console or a PC, high-end. The tradeoff is the latency of the stream, but the companies are working to overcome these problems.
None of these services, however, will never get on the App Store, at least until Apple will not change a few rules. Choice somewhat remote, since the company has recently launched the subscription-based service Apple Arcade. Of course, Apple Arcade works in a different way from the services of game streaming, but in fact collects, however, several titles that can be played only by subscription. In short, Apple Arcade is not a streaming service, since the games are downloaded and saved locally.
Not surprisingly, services similar to Apple Arcade as GameClub are normally available on the App Store, in spite of some difficulties in the approvals up to the end.