In this video, we discuss what exactly Ionic 3 is and what the difference will be to Ionic 2. The short answer is: it's just an update to the same framework, it's not a whole new framework - Ionic is just using a different versioning system now (SemVer).
Blog post: https://www.joshmorony.com/what-does-ionic-3-mean-for-ionic-2/
Learn Ionic: https://www.joshmorony.com/building-mobile-apps-with-ionic-2/