When it comes to Stadia and xCloud, Android has been the go-to place for these experiences, but Apple was supposed to join in on the fun by allowing the two services on iOS.
At least that's what some iOS users were hoping for. Apple just shut out Stadia and xCloud from of iOS. Stating that the services like them "violate its App Store policies." xCloud for a time, was available to iOS users. During the earlier parts of the xCloud preview. But the contract period for that is now over and Apple won't be renewing.
Stadia, for its part, has never had access to iOS and its legion of users. And it never will. Not for the foreseeable future anyway.
Apple won't allow Stadia or xCloud because it can't manually review every game
According to Business Insider, The reason Apple is blocking cloud gaming services from iOS is because it can't individually review each game on those services.
Apple's statement on the matter is such that users trust its platform because it's able to look at each game that comes in for approval. Allowing it to make a judgement call on if its safe to distribute. Because it can only review the xCloud app or Stadia app, and not the games themselves, this is where Apple says the violation lies.
The main problem Apple seems to have with cloud gaming services is that they don't act more like full remote desktop apps. Apple also isn't getting any revenue from the money people would spend by subscribing to them.
xCloud, GeForce NOW, and Stadia all have you signup prior to access through the app. And those subscription charges wouldn't go through Apple. Stadia offer the capability to purchase games through its app, but not directly through the App Store. Which is where Apple would get its cut.
Apple doesn't specifically mention anything about revenues. Its official statement is instead focused on the trust and security of its users, and fairness of its ecosystem's developers.
Does this mean iOS will never have access to cloud gaming services?
Not really. For the time being, neither Stadia, nor xCloud, nor GeForce NOW are available on iOS.
Shadow however is, and it's essentially the same type of service. At least it's marketed as the same type of service. It's positioned to users as cloud gaming. But functionally, it's a full remote desktop app.
The kicker is that its hardware that users remote into are all gaming PCs. So full remote desktop or not, most subscribers of Shadow are likely going to use it for gaming and little else.
That means there is a possibility down the road that xCloud, Stadia, and GeForce NOW could be slightly altered to fit within the guidelines for iOS access. Just not for the time being.