As a result of Angular 5’s delay, Angular 6 should arrive in March or April 2018, followed by Angular 7 in September or October 2018. Each version is promised to be backward-compatible with the prior release.
Angular 5’s promised capabilities include building progressive web apps as well as a build optimizer and accommodations for Material Design components.
After taking multiple years between the first version of Angular and the rewritten Angular 2, Google pledged to do twice-a-year upgrades. Google then skipped over the Angular 3 designation and went right to Angular 4 last year, to align the framework with the version number of the router it used.