Problem/Motivation
- CKEditor 4 security support is guaranteed "only"until 2023.
- CKEditor 5 is an entirely new architecture, so contrib modules that use the CKE4 API (e.g., to implement editor plugins) will not work on CKE5. Therefore, upgrading Drupal from CKE4 to CKE5 in a Drupal 9.x minor would violate semver.
- So, ideally we need to either decide to EOL D9 in 2023 (which likely means release D10 in 2022), or else we need to upgrade to CKE5 in 9.0 (which means adding it as a side-by-side option alongside CKE4 prior to 8.LAST).
- Knowing D9's EOL date range might affect our other vendor library decisions too.
Proposed resolution
Remaining tasks
Discuss.