Angular is a popular framework for creating front end web applications. These run in the browser and provide great experiences for headless CMS scenarios and custom web applications alike. Together with server side rendering coming in Angular 2, it is perfect for building fluent content experiences on Drupal 8 REST APIs.
The Drupal community has already gone through years of waiting for a large release. Finally in late 2015 Drupal 8 was released. With version 2, the Angular community is going through the same thing. The new version has been long time in the making and will be a technical revolution.
With the development tools already very mature, the Angular team is mostly working on fixing the final kinks and edge cases. According to the latest weekly meeting notes from the Angular 2 team, it looks like Angular 2 is set for September 2016.
So with Angular 2 reaching Release Candidate (RC) status, then it means that the release is already in sight and large changes in the framework are pushed to later versions. That is why if you're looking to start a new Angular 2 project with Drupal 8, then it is likely that you can already start working on these today.