Additional target audiences for Workflow Engine

Hi aXcelerate team,

We have been experimenting with the Workflow Engine, and are really impressed with it so far. I have been throwing around ideas for workflows that could streamline our communications with Workshop and Class participants, and have identified some interesting use-cases that I thought you might be able to cover off in future refinements. We like the ability to differentiate between All, Enrolled, Completed, etc statuses and tailor our message to these different audiences, and we have a few more examples of different sub-sets we would like to see on the list:
* Learners without a validated USI
* Learners who have an unpaid course invoice
* Learners who have/have not been granted credit for some course outcomes (on an Recognition of Prior Learning basis).
* Workshop learners who have not completed an associated piece of eLearning (served from aXcelerate)

This could be implemented by adding each of these groups to the list of selectable audiences, or the same (and possibly much more) could be achieved by creating a second layer of conditional filtering. We'd be happy either way, and I am sure the dev team will have some ideas as to their preferred implementation method.

Cheers

Chris