We got most of the way to removing the AbstractPageAction. We did this by introducing the replacement AbstractPageAwareAction which is intended to only implement enough to satisfy the PageAware interface. The remaining issues above detail what is left to achieve this.
The migration policy involved changing any class to extend the AbstractPageAwareAction and fix any missing references. If appropriate, these were extracted into beans, or changed to private methods and moved to a more appropriate class.
We used our velocity usage audit log periodically to check for usages within our velocity templates.
We moved enough classes so we could deprecate AbstractPageChangeAction, AbstractFileAttachmentAction, and AbstractEditAttachedFileAction.
Related Doco:
http://confluence.atlassian.com/display/DOC/XWork-WebWork+Plugins
Still holds true. Almost all the changes were made in the AbstractPageAction and below and (for now) ConfluenceActionSupport still needs to be used.