I have no doubt Google will not use iOS default GUI components. They will come up with some sort of abomination that superficially looks like the native iOS components but are off in every way when you look closely, like Qt does.
> App bars become UINavigationControllers. Standard controls just need light branded touches. Lists can align with modern UITableView and list-based collection view APIs. Menus are just UIMenus.
> And the best code is often no code :)
> The time we're saving not building custom code is now invested in the long [...]
Also, the existing MDC components are already built on top of UIKit - things like MDCButton is a UIButton subclass (with a lot of stuff added on). Same for textfields, collectionview cells, etc. There's no from scratch reimplementation of Apple's UI components that I'm aware of, just extensions to make the Material design stuff happen.