Assign authorized users to the different workflow steps

It is currently not possible to assign users on certain steps on a given workflow instance. So all users who are "Publishers" are automatically assigned to the task (and currently no one as there is no "Validator" role and oly a last step Publisher one). Usually the role is more a way to define who can "potentially" be responsible of performing such or such actions on such or such pages. But one may perhaps want to precisely define that "Jenifer" (and not "raoul" - both beloing to the Publisher role) has to perform the review.

Of course Raoul may take the initative (if Jenifer is in holidays or so), but wouldn't it be nice (and perhaps more manageable) to let the editor who define the workflow choose among all publishers the one which are entitled to perform the 1 and the 2 steps? (as it was the case beofre excpeted that you would need the prior permissions on the given step to be selected)?