Our Sector frontend team has done the magic! Sector is one more distribution to go Radix.
The 5.0.x-dev branch - we have adapted to the new semantic versioning dropping the Drupal prefix - now includes the new Sector Radix Starter theme, a sub theme of the also included Radix theme.
The team sums up what is in the box in Introducing the Sector Radix Starter theme.
The 5.0.x branch will be come our main branch once the housekeeping - module and security updates - are completed. After both the 5.0.x branch and the 8.x-4.x, are up-to-date we will drop the support for the 8.x-3.x branch.