The Drupal 8 to Drupal 9 upgrade path represents a big change for the Drupal world. The big change is that…your organization’s website won’t require a big change. The first iteration of Drupal 9 is just Drupal 8 with all of the deprecated code removed, mimicking Symfony’s model of major release upgrades.
This is good news. Keeping your platform up-to-date with the next version is no longer an “all hands on deck” situation.