Action::factory() removes Page support and will only support Article as a parameter, thus Article will now be passed into the action overrides callbacks. The documentation for the callbacks state that they should work with any Page instance, but we need to validate that it's the case first and check if converting deprecated WikiPage into Article in Action::factory wouldn't break the callbacks.
Check action overrides for Page parameter
https://codesearch.wmflabs.org/deployed/?q=function%20getActionOverrides&i=nope&files=%5C.php%24&repos=