We have done lot of refactoring in the kubernetes package in 6.3 - https://github.com/cdapio/cdap/pull/12522
In release 6.1.4 we added ability to run previews in their own pods - https://github.com/cdapio/cdap/pull/12576
However because of the refactoring on 6.3, the preview PR from 6.1.4 cannot be cherry-picked as it is and will need to write implementation conforming to the new code in kubernetes package.
As a part of this we will also need to add stopping of distributed preview.
We should also remove the defaulting of preview-runner to use priority-low. If priority class is provided in cdap-site config use it else leave it blank.