I started porting Climateer from UIKit to SwiftUI and I’m using it as an experiment to check the feasibility of doing it top-down. I started with the App struct holding everything else, rewriting some views in SwiftUI and wrapping others in UIViewControllerRepresentable for the time being.
It’s like having two entry points into my app. I can comment out @UIApplicationMain in my AppDelegate, uncomment @main in my App struct, et voilà, I run from SwiftUI. No complex project configuration or plist incantation needed. Apple did a nice job making it easy to go full-SwiftUI at the app level.