Workflow assign user to handle node in given state
I am developing a module that address that very issue and some other things. Besides it is on sandbox yet, it is fully usable (I am using it on production).


  Workflow Hide Fields is an addon to the Workflow module.


You can clone it:

git clone --branch 7.x-1.x git://git.drupal.org/sandbox/fpap/2575131.git


And can visit the module page.