Gary, by looking at the code it seems the out of the box usage of the exludedUsers is not implemented not on the handler side nor on the task service side.
That should not be too much of a problem to add that support and the value out of it could be really great. Of course these are my findings, perhaps I missed something.
Another thing I found that could be useful (but perhaps too big limitation for your case) is that you could apply rules before adding a task, in case rules are not satisfied task won't be created.