After 20 years of thinking "Apple is taking gaming seriously this time!" every 3 years, then getting __excruciatingly__ burned, I've given up. They'll build it before they buy it.
Based on how they've backed off SpriteKit and SceneKit, I really don't think they will try to build a game engine. Bringing on the big game developers requires a cross-platform engine. Like Unity, one that can target Nintendo Switch, Xbox, Playstation, etc. Any money they pour into an effort like that would cannibalize sales on their own devices.