When working with YAWL, I found that it would be advantageous to have a drop down list of users in a task. The list would be used to assign the next work item to the selected user. I know it is possible to assign task via the resource service, but the resource service only complicates things for users. Hence we use the gadgetfeeder to display available work items for users without showing the rest of the resource service for them altogether.
This is also important, because not everybody, who should have the capability to assign work items, should have the admin right needed to do it.
In that context a custom drop down list with users can be made for each worklfow, but every time the list of users change, the workflow would need to be adjusted.
Therefore, I think it would be a good feature to have a list like that in a workflow.