So far, in this book, we have gone through the process of building apps with Ionic 2, without the knowledge of Ionic 1. But as far as the real world goes, there are a few thousand apps already deployed with Ionic 1. Those apps can take advantage of the improved features of Ionic 2 to make the app experience better.
Migrating code in the world of software is a daunting task. In our case, the migration is even more complex because we are not just upgrading the libraries of Ionic 1 to Ionic 2 but upgrading the language itself on which these are written for example, ES5 to ES6 and TypeScript.
The new ecosystem for JavaScript apps primarily revolves around ES6, TypeScript, and Web Components. Adapting to these to take advantage of the latest technologies is what Angular 2 has done. Ionic 2 has also done this.
IMHO, with so many changes, migrating a fully functioning app from Ionic 1 to Ionic 2 should be...