Supersite for Windows posted As Windows 10 RS3 Development Winds Down Windows Insiders Get a Chance to Skip Ahead to RS4 A quote from the article:

This will also allow Insiders to continue testing early updates for first party apps

As the Redmond company gets ready to wrap up development on the Fall Creators Update, they are offering a limited number of Windows Insiders to skip ahead and begin testing the first builds for the fifth major feature update for Windows 10.

 As Windows 10 RS3 Development Winds Down Windows Insiders Get a Chance to Skip Ahead to RS4 @ WinSupersite