Issue 1: My aim is that when a user submit a post (aka create it, the very first step) in the workflow, any other user can claim the post and start writing on next step.
- this is a scenario when there are multiple authors on a given post.
By default, the "Author" role is not allowed to edit posts/pages from another author. So, I would suggest installing the "User Roles Plugin" - http://wordpress.org/extend/plugins/user-role-editor/ and change the "Author" capabilities to include "edit_others_post" and "edit_others_pages".
By doing so, a post submitted by Author 1 can be worked on by Author 2.
As far as workflow is concerned there are two ways to achieve this.
Assignment(Initiate) --> Assignment(Build) --> Review --> Publish
Here, Admin creates a blank post (may be with just a title and no content) and then submits to the workflow and assigns it to a particular author to initiate it. Author 1 initiates writing a post and then submits the post to multiple Authors. As a result all the authors will see the assignment in their inbox. The first author to claim the post will continue to build the post and then submit for review.
Assignment(Build) --> Review --> Publish
In this, the post is submitted to the workflow AFTER its been already initiated.
Basically, Author1 creates a post and then submits it to the workflow. Again while submitting to the workflow he/she selects all the available authors from the list.
Issue 2: But, on some workflow, I want only one user to be able to publish post (last step), as the user is the editor in chief of that particular topic.
Right now, as you might have already noticed, the plugin is role-based. That is, all the users who hold a given role will be shown in the selection list. The user from the current step can choose from the list of users and sign off.
If the intention is to relate a post to a particular "Editor-in-chief", given that there are multiple users who hold such a role, then I will have to enhance this plugin to do so. This would be a nice feature to have.
This is basically a concept where the "delegation" is already been decided BEFORE the post goes through the workflow.
Hopefully this answers your questions. Do let me know if you have additional questions.
Thanks for your review comments and support.