[myoon]

The path provided is being able to load Angular 9 components into AngularJS components relatively seamlessly. This is helpful, but it's almost certainly a big leap to get your codebase compiling under angular-cli. If you manage it though, you can, in theory, do a bottom-up replacement of all your AngularJS components.

Another thing to think about though is how you're currently doing state management. Angular 9 is all about RxJS, and if you're currently managing state without it, your migration will be that much harder.