In #1499596: Introduce a basic entity form controller we unified the generation of entity forms but the actions associated to the various entity-specific forms still need to be unfied and the related code moved to the base implementation. We need some discussion about the preview action, which is available in a couple of entity types (comment and node) only: it might make sense to move preview code to the base implementation if it can be generalized enough.

Comments

Would this also be the issue for

  public function save(array $form, array &$form_state) {
    // @todo Perform common save operations.
  }
  public function delete(array $form, array &$form_state) {
    // @todo Perform common delete operations.
  }

?

Yes, definitely so.

Also most of core entities use confirmation of delete, so base controller should care about that

Yes

It seem that we could close this in favor of #1839516: Introduce entity operation providers