This is the Epic to collect issues required to remove the Classic theme from Moodle.  

The time line will be 

• From Moodle 5.0 until Moodle 5.3 Classic theme will continue to be supported
  • Testing will continue as it is currently conducted with every release
  • New functionality will be supported in Classic theme
  • Accessibility bugs and significant issues will continue to be addressed 
  • Minor and more trivial issues will be deprioritised

• As part of the Moodle 6.0 release, Classic theme will be moved out of core and into the plugins directory.
  • No new features will be supported in Classic for the Moodle 6.0 release and beyond
  • Any remaining issues that only affect Classic will be closed
  • Some CSS and code cleanup will occur in Moodle 6.0 and subsequent versions, these will occur in line with the current deprecation policies.

This will give users essentially 2 LTS versions (4.5 and 5.3) before customer need to move which is close to 4 years.